* Do not require gtk-doc to be installed.
* Use FindPackageHandleStandardArgs in FindGtkDoc.cmake.
* Fix installation (wrong source path).
* Don't install neither the documentation nor the desktop file on Windows.
FindGTK2.cmake required a change for successful program compilation.
It seems that gdk_pixbuf has been put as a separate library.
The new tools also generate a slightly different version
of marshallers, so I've added it to the tree.
