Fix for ticket #1036: Add proxy-style (absolute-url) requests support

Add absolute-url support as described in ticket #1036.
1. Simply parse the uri startswith 'http' or 'https' via urlparse.urlparse and convert it into relative-path
2. add several test cases in  httpserver_test
We should do something to make the rest of the parsed url available.  RFC 2616 section 5.2 says that the Host header should be ignored when an absolute url is given and the host from this url should be used instead.