tests/readlink.py

dispatch: make "_checkshellalias" reusable regardless of adding aliases

To reduce changes in the subsequent patch fixing issue4355, this patch
makes "_checkshellalias" reusable regardless of adding aliases.

In this patch, alias definitions are added and restored, only when
"precheck=True".

#!/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)