* Makefile.mingw: updated for 7.4 windows
	* boards/images/README:
	* boards/images/enumerate_background.png: Remade by by Herve Chanal.
	* src/boards/click_on_letter.c: (start_board), (end_board),
	(sounds_are_fine), (click_on_letter_create_item), (conf_ok): now sounds is muted
	* src/boards/memory.c: (start_board): added a dialog when sounds is not activated that the activity cannot be played.