Use xi:include instead of entities to ease maintenance and speed up

Use xi:include instead of entities to ease maintenance and speed up

	* gdk-pixbuf/gdk-pixbuf-csource.xml:
	* gdk-pixbuf/gdk-pixbuf-from-drawables.sgml:
	* gdk-pixbuf/gdk-pixbuf-query-loaders.xml:
	* gdk-pixbuf/gdk-pixbuf-rendering.sgml:
	* gdk-pixbuf/gdk-pixbuf.sgml:
	* gdk-pixbuf/porting-from-imlib.sgml:
	* gdk/gdk-docs.sgml:
	* gdk/multihead.sgml:
	* libgail-util/gail-libgail-util-docs.sgml:
	  Use xi:include instead of entities to ease maintenance and speed up
	  documentation build. Fixes #540967

svn path=/trunk/; revision=21304