Support usernames and passwords in URLs

[mlococo]

While not optimal from a security perspective, it is moderately common for http clients to send URLs that contain usernames and passwords such as http://name:[email protected]/somepath/. Polipo parses these URLs assuming that the colon is always a separator between host and port as in http://example.com:8080/somepath. Depending on the content of the request, this can result is several different errors, a hostname lookup error using the password as a hostname, a forbidden port error (if the password begins with a number), probably other conditions are possible. It would be good if polipo was able to parse URLs containing usernames and passwords in them.