Eliminate all but three compiler warnings.

Most are banished by use of a new UNUSED macro that expnds to the
right GNU C++ attribute but an empty string elsewhere.  I have the
definition being generated into config.h, which therefore has to be
included a few places it wasn't before.  There might be a better place
to put it.

configure.ac

@@ -807,7 +807,18 @@ if test "x$lite" = "xno"; then
     fi
 fi
 
+#######################################################################
+# Make UNUSED available for suppressing warnings of unused parameters #
+#######################################################################
 
+AH_VERBATIM([_GNU_SOURCE],
+          [/* Macro for declaring function arguments unused. */
+#if defined(__GNUC__)
+#  define UNUSED __attribute__((unused)) /* Flag variable as unused */
+#else /* not __GNUC__ */
+#  define UNUSED
+#endif
+])
 
 #######################################################################
 # Tune gettext stuff for our needs                                    #

src/ai_python.hpp

@@ -5,6 +5,7 @@
 
 #include "ai_interface.hpp"
 #include "menu_events.hpp"
+#undef _POSIX_C_SOURCE	// avoids a spurious compiler warning
 #include <Python.h>
 
 typedef struct {

src/construct_dialog.cpp

@@ -40,6 +40,7 @@
 #include "widgets/progressbar.hpp"
 #include "widgets/textbox.hpp"
 #include "wassert.hpp"
+#include "config.h"	// For UNUSED
 
 #include "sdl_ttf/SDL_ttf.h"
 
@@ -88,7 +89,7 @@ private:
 		}
 	}
 
-	bool can_execute_command(hotkey::HOTKEY_COMMAND cmd, int index=-1) const
+	bool can_execute_command(hotkey::HOTKEY_COMMAND cmd, int index UNUSED) const
 	{
 		return (topic_.empty() == false && cmd == hotkey::HOTKEY_HELP) || cmd == hotkey::HOTKEY_SCREENSHOT;
 	}

src/events.cpp

@@ -243,8 +243,8 @@ bool has_focus(const handler* ptr, const SDL_Event* event)
 	} else if(!event_contexts.back().handlers[index]->requires_event_focus(event)) {
 		//if the currently focused handler doesn't need focus for this event
 		//allow the first-in interested handler to take care of it
-		for(int i=0; i<event_contexts.back().handlers.size(); i++) {
-			if(i != index && event_contexts.back().handlers[i]->requires_event_focus(event)) {
+		for(unsigned int i=0; i<event_contexts.back().handlers.size(); i++) {
+			if(i != (unsigned)index && event_contexts.back().handlers[i]->requires_event_focus(event)) {
 				//focus_handler(event_contexts.back().handlers[i]); //steal focus?
 				return event_contexts.back().handlers[i] == ptr;
 			}

src/floating_textbox.cpp

@@ -16,6 +16,7 @@
 
 #include "font.hpp"
 #include "preferences.hpp"
+#include "config.h"	// For UNUSED
 
 namespace gui{
 	floating_textbox::floating_textbox() : box_(NULL), check_(NULL), mode_(TEXTBOX_NONE), label_(0)
@@ -100,7 +101,7 @@ namespace gui{
 		update_location(gui);
 	}
 
-	void floating_textbox::tab(std::vector<team>& teams, const unit_map& units, display& gui)
+	void floating_textbox::tab(std::vector<team>& teams, const unit_map& units UNUSED, display& gui)
 	{
 		if(active() == false) {
 			return;

src/hotkeys.cpp

@@ -506,7 +506,7 @@ void key_event_execute(display& disp, const SDL_KeyboardEvent& event, command_ex
 	execute_command(disp,hk->get_id(),executor);
 }
 
-bool command_executor::execute_command(HOTKEY_COMMAND command, int index)
+bool command_executor::execute_command(HOTKEY_COMMAND command, int index UNUSED)
 {
 	switch(command) {
 		case HOTKEY_CYCLE_UNITS:

src/image.cpp

@@ -448,7 +448,7 @@ void set_colour_adjustment(int r, int g, int b)
 	}
 }
 
-void set_image_mask(const std::string& image)
+void set_image_mask(const std::string& image UNUSED)
 {
 
 	//image_mask are blitted in display.cpp

src/multiplayer_ui.cpp

@@ -26,6 +26,7 @@
 #include "video.hpp"
 #include "replay.hpp"
 #include "wml_separators.hpp"
+#include "config.h"	// for UNUSED
 
 #define LOG_NG lg::info(lg::engine)
 #define LOG_NW LOG_STREAM(info, network)
@@ -41,7 +42,7 @@ namespace {
 										   item_size_(empty_rect) 
 		{}
 		virtual void init();
-		virtual SDL_Rect item_size(const std::string& item) { return item_size_; }
+		virtual SDL_Rect item_size(const std::string& item UNUSED) { return item_size_; }
 		void set_width(const int width) { item_size_.w = width; }
 	private:
 		SDL_Rect item_size_;

src/pathfind.cpp

@@ -20,6 +20,7 @@ See the COPYING file for more details.
 #include "pathfind.hpp"
 #include "util.hpp"
 #include "wassert.hpp"
+#include "config.h"	// For UNUSED
 
 class gamestatus;
 
@@ -516,7 +517,7 @@ shortest_path_calculator::shortest_path_calculator(unit const &u, team const &t,
 {
 }
 
-double shortest_path_calculator::cost(const gamemap::location& src,const gamemap::location& loc, const double so_far, const bool isDst) const
+double shortest_path_calculator::cost(const gamemap::location& src UNUSED,const gamemap::location& loc, const double so_far, const bool isDst) const
 {
 	wassert(map_.on_board(loc));
 

src/play_controller.cpp

@@ -23,6 +23,7 @@
 #include "sound.hpp"
 #include "variable.hpp"
 #include "wassert.hpp"
+#include "config.h"	// For UNUSED
 
 #define LOG_NG LOG_STREAM(info, engine)
 
@@ -297,7 +298,7 @@ void play_controller::init_gui(){
 	}
 }
 
-void play_controller::init_side(const unsigned int team_index, bool is_replay){
+void play_controller::init_side(const unsigned int team_index, bool is_replay UNUSED){
 	log_scope("player turn");
 	team& current_team = teams_[team_index];
 
@@ -875,7 +876,7 @@ bool play_controller::in_context_menu(hotkey::HOTKEY_COMMAND command) const
 
 std::string play_controller::get_action_image(hotkey::HOTKEY_COMMAND command, int index) const
 {
-	if(index >= 0 && index < wml_commands_.size()) {
+	if(index >= 0 && (unsigned)index < wml_commands_.size()) {
 		wml_menu_item* const& wmi = wml_commands_[index];
 		if(wmi != NULL) {
 			return wmi->image.empty() ? game_config::wml_menu_image : wmi->image;

src/show_dialog.cpp

@@ -38,6 +38,7 @@
 #include "widgets/progressbar.hpp"
 #include "widgets/textbox.hpp"
 #include "wassert.hpp"
+#include "config.h"	// For UNUSED
 
 #include "sdl_ttf/SDL_ttf.h"
 
@@ -322,7 +323,7 @@ private:
 		}
 	}
 
-	bool can_execute_command(hotkey::HOTKEY_COMMAND cmd, int index=-1) const
+	bool can_execute_command(hotkey::HOTKEY_COMMAND cmd, int index UNUSED) const
 	{
 		return (topic_.empty() == false && cmd == hotkey::HOTKEY_HELP) || cmd == hotkey::HOTKEY_SCREENSHOT;
 	}

src/sound.cpp

@@ -618,7 +618,7 @@ void write_music_play_list(config& snapshot)
 void reposition_sound(int id, unsigned int distance)
 {
 	audio_lock lock();
-	for(int ch = 0; ch < channel_ids.size(); ++ch) {
+	for(unsigned int ch = 0; ch < channel_ids.size(); ++ch) {
 		int& ch_id = channel_ids[ch];
 		if(ch_id == id) {
 			if(distance >= DISTANCE_SILENT) {