URL parser: cut off '#' fragments from URLs (better)

The existing logic only cut off the fragment from the separate 'path'
buffer which is used when sending HTTP to hosts. The buffer that held
the full URL used for proxies were not dealt with. It is now.

Test case 5 was updated to use a fragment on a URL over a proxy.

Bug: http://curl.haxx.se/bug/view.cgi?id=3579813