Fix all-gtype-instances initialization

- Lazily initialize it
- GObject has GTypeInstance as a parent
Remove gdkpixbuf jam file and undefined functions in gio
Declare <GTypeInstance> as an open C-subtype
Change return type of g-object-ref-sink to <C-void*>

This was causing an infinite loop in make.
Update Gtk+ libraries

This update:

- fixes object properties
- improves names of slots and variables
Merge pull request #523 from fracek/glue-fixes

Glue fixes