tests/readlink.py

histedit: rename `tip` to `topmost`

I expected `tip` to be repo's tip when it was the rewritten set tip. I rename
the variable to the less ambiguous `topmost`.

#!/usr/bin/env python

import errno, os, sys

for f in sys.argv[1:]:
    try:
        print f, '->', os.readlink(f)
    except OSError, err:
        if err.errno != errno.EINVAL:
            raise
        print f, 'not a symlink'

sys.exit(0)