add -quick option to muddle status

check only git repositories
check only if local head of branch
is different from the last known state of the remote
report problem if vcs is not git or file.

used while checking if local changes have been pushed
work-around: status --porcelain will not report if we're ahead or behind the view of the remote

compare head to version recorded for origin repository
change pull to push on muddle status -quick warning message
Merge branch 'quick-status' into quick-status-revisited

Conflicts:
	muddled/commands.py
	muddled/vcs/svn.py
	muddled/version_control.py
resolved
Missed merge fix
Improve the "status -quick" diagnostic message