Handle subdirectories with match.py script

[irreality177]

If directory that contains messages also contains subdirectories the match.py script exits with Traceback like the following:

Traceback (most recent call last):
  File "scripts/match.py", line 118, in <module>
    main()
  File "scripts/match.py", line 95, in main
    for msgf in message_list:
  File "scripts/match.py", line 26, in __call__
    msgf = super(MessageList, self).__call__(path)
  File "/usr/lib/python2.7/argparse.py", line 1142, in __call__
    raise ArgumentTypeError(message % (string, e))
argparse.ArgumentTypeError: can't open '/root/msgs/1': [Errno 21] Is a directory: '/root/msgs/1'

Such case should be handled.