Since we're dynamically loading objects, after the g_type_init()
change, we now need to ensure people building with --as-needed don't
lose the DT_NEEDED on libgobject.
https://bugzilla.gnome.org/show_bug.cgi?id=691077
Very many testcases, some GLib tools (resource compiler, etc) and
GApplication were calling g_type_init().
Remove those uses, as they are no longer required.
https://bugzilla.gnome.org/show_bug.cgi?id=686161
If there are no modules installed then the most appropriate thing is to
have no cachefile instead of an empty one. This unbreaks the "clean
directory after 'make uninstall'" check that automake does.
https://bugzilla.gnome.org/show_bug.cgi?id=671664
