Fix --enable-gtk-doc build

Fix --enable-gtk-doc build

2007-03-20  Tommi Komulainen  <tommi.komulainen@nokia.com>

	* doc/gtk-doc.make: Update from gtk-doc 1.7, and fix '*.sgml'
	prerequisite with $(wildcard) to work in absence of any files.
	* doc/Makefile.am (MAINTAINERCLEANFILES): Add 'tmpl/*.sgml' here, it
	used to be handled in the modified gtk-doc.make
	(HTML_IMAGES): Fix images locations by adding missing 'images/'
	* doc/visual_index.xml: Remove extraneous 'html/' from image
	references that were breaking the generated gallery page.