tests/readlink.py

run-tests.py: work when --with-hg is set to system hg

Previously we'd always assume that --with-hg is a script in a user directory,
and would write out a 'python' symlink to the same location. That didn't work
if --with-hg was set to a system installation of hg, e.g. /usr/bin/hg.

Introduce a TMPBINDIR directory which is used to write out the python symlink.

#!/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)