Fixed problem with handling URLs that have no path and no trailing slash

In case of URL like http://example.com reppy checks for 'm' instead of '/'.
I fixed path extraction process and added tests for that case.

This is a problem when robots.txt has "Disallow: /" rule for which reppy fails to check permission for empty path or, when using full URLs, for URL with no path and no trailing slash, like http://example.com