Add og_set_group_context to admin functions

Hello! This is a really nice module, with fit perfectly to my projects need. I have done some tweaking though, but have a small suggestion. When you go to the admin functions like og_bookmarks/%/edit it would be nice to set the active group. Cause it is a og group, and lots of things are often dependent on this condition, then i.e. menus and blocks. Therefore I suggest a og_set_group_context on those functions. I have done it, and it works perfectly. The node is already loaded.