Xcode4+ linker workaround for pre-Lion SDKs
Upgrade gtk+-3.0 to gtk+-3.10.7

Needed to pick up gnome icons by default.
Add gnome theme

Gtk+-3.10 and later requires "gnome" themes for some of its standard
icons. This change adds those packages and make the core ones a
dependency of meta-gtk-osx-gtk3.