synced vcs with upstream

- moved subprocessio module to VCS
- many small changes to make embedded vcs as similar to to external lib
- use only absolute imports
- patch vcs config during load pylons env

further cleanup of UsersGroup

Renaming some names ... but trying not to change API or database scheme.

RhodeCode now has a option to explicitly set forking permissions. ref #508
- changed the way permissons on users groups behave. Now explicit set on user
is more important than permission set on users group

commit less models
- models don't do any commits(with few exceptions)
- all db transactions should be handled by higher level modules like controllers, celery tasks

removed users_group controller in replace for model methods,
fixed tests

Added CheckSessionFlash into init.
Added repo_groups_test controller.
Renamed users_groups test controller