Use getopt_long() instead of getopt_long_only() to parse arguments.

getopt_long() does not allow long options with a single '-'. It is a less
flexible than getopt_long_only(), but fixes the error message
"option '-l' is ambiguous" with MSYS on Windows.
Merge pull request #46 from svnieuw/master

Use getopt_long() instead of getopt_long_only() to parse arguments.