Bug 6826: Build messages in about box

	Added --with-build-message to ./configure.  A build message will
	display in the about box if no EAZEL_TIMESTAMP (used by hourly builds)
	has been set.

	The default build message for CVS builds "Development Version"

	* acconfig.h:
	* configure.in:
	* libnautilus-extensions/nautilus-file-utilities.c:
	(nautilus_get_build_message):
	* libnautilus-extensions/nautilus-file-utilities.h:
	* src/nautilus-window-menus.c: (help_menu_about_nautilus_callback):