tag: abort if not at a branch head (issue2552)...
tag: abort if not at a branch head (issue2552)
Since it's usually only desirable to make tag commits on top of branch
heads, abort if the working dir parent is not a branch head. -f/--force
may be passed to commit at a non-head anyway.
Does not abort if working dir parent is a named branch head but not a
topological head.
