#6 Add version info reporting

[Vincent Legoll]

When I wanted to report a bug I stumbled upon the fact that gquilt does not report its version.

So here is a patch implementing "-v" and "--version" command-line options
and additionally it reports version in usage() too.

BTW I fixed the use of sys.argv after getopt parsing, since it's now conceptually not right to hardcode sys.argv[1], if we add more command-line options in the future.