Blender Git Loki

Adding some simple but very convenient selection
functionality for the UV editor:

* A "Select->Pinned UVs" command (Shift P) that
selects all the visible pinned UVs
* A "Select->Border Select Pinned" tool (Shift B) that
works just like the normal border select tool, but only acts on pinned UVs

This is really useful when using LSCM, I only want to
touch the pinned UVs and then recalculate.