GUI2/Modal Dialog, Modeless Dialog: made window_ a protected class member

This will allow direct use of the window pointer without binding in hundreds of different
callbacks just because we want to use it for, say, find_widget.

This is just the base change. I still might change my mind as to this method, and I have
yet to undertake any refactoring around this.

modal_dialog::get_window and modeless_dialog::get_window remain.

src/gui/dialogs/modal_dialog.hpp

@@ -325,10 +325,11 @@ protected:
 		return register_label(id, mandatory, filename);
 	}
 
-private:
+protected:
 	/** The window object build for this dialog. */
 	std::unique_ptr<window> window_;
 
+private:
 	/** Returns the window exit status, 0 means not shown. */
 	int retval_;
 

src/gui/dialogs/modeless_dialog.hpp

@@ -84,10 +84,11 @@ public:
 		return window_.get();
 	}
 
-private:
+protected:
 	/** The window, used in show. */
 	std::unique_ptr<window> window_;
 
+private:
 	/** The id of the window to build. */
 	virtual const std::string& window_id() const = 0;