use a mask of 0xffffffff instead of 0xffff, since there are 22 flags

use a mask of 0xffffffff instead of 0xffff, since there are 22 flags

Sat Feb  7 11:33:08 1998  Owen Taylor  <owt1@cornell.edu>

	* gdk/gdkgc.c (gdk_gc_copy): use a mask of 0xffffffff
	  instead of 0xffff, since there are 22 flags currently
	  defined. (From: Jon Trowbridge <trow@emccta.com>)