Implement automatic module license checking according to new GNU

guidelines.

	* grub-core/kern/dl.c (grub_dl_check_license): New function.
	(grub_dl_load_core): Use grub_dl_check_license.
	* include/grub/dl.h (GRUB_MOD_SECTION): New macro.
	(GRUB_MOD_LICENSE): Likewise.
	(GRUB_MOD_DUAL_LICENSE): Likewise.
	All modules updated.

grub-core/commands/memrw.c

@@ -23,6 +23,8 @@
 #include <grub/env.h>
 #include <grub/i18n.h>
 
+GRUB_MOD_LICENSE ("GPLv3+");
+
 static grub_extcmd_t cmd_read_byte, cmd_read_word, cmd_read_dword;
 static grub_command_t cmd_write_byte, cmd_write_word, cmd_write_dword;