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.
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24