Show the main menu several times faster...

...by skipping terrain rules (useless there)

This also speed up the use of '--load'. Add a new define MAIN_MENU for
this.

data/_main.cfg

@@ -57,7 +57,9 @@
 
 # Include the terrain-graphics definitions after the campaigns so campaign specific
 # terrains work properly.
+#ifndef MAIN_MENU
 {core/terrain-graphics.cfg}
+#endif
 
 [binary_path]
     path=data/core

data/core/_main.cfg

@@ -3,12 +3,15 @@
 
 # wmlscope: set export=yes
 
+#ifndef MAIN_MENU
+{core/terrain-graphics/}
+#endif
+
 {core/macros/}
 {core/about.cfg}
 {core/help.cfg}
 {core/hotkeys.cfg}
 {core/terrain.cfg}
-{core/terrain-graphics/}
 {core/units.cfg}
 {core/editor/}
 

src/game.cpp

@@ -595,6 +595,9 @@ bool game_controller::init_config(const bool force)
 	if (jump_to_editor_)
 		cache_.add_define("EDITOR");
 
+	if (!multiplayer_mode_ && !test_mode_ && !jump_to_editor_)
+		cache_.add_define("MAIN_MENU");
+
 	load_game_cfg(force);
 
 	const config &cfg = game_config().child("game_config");