install of libraries fails without gtk-doc

[Jasper Huijsmans]

Hi all, especially benny,

It seems without gtk-doc the install of our libraries fails with a 
missing ./html/index.sgml file. I don't really see where and when this 
is suposed to be created, nor why it is not included in the dist tarball.

Any ideas?

What is this file used for anyway? for help browsers who want to use the 
sgml directly?

	Jasper