Rewrite HTTP Host header in requests to named exit nodes (.foobar.exit)
When the user types a URL with a named exit node into the address bar (e.g. http://www.torproject.org.foobar.exit/), torbutton currently includes the exit node name in the HTTP "Host" header in the request. Instead, torbutton should rewrite the HTTP Host header to remove ".foobar.exit", so that it only contains the original hostname (i.e. "Host: www.torproject.org"). The current behavior leads to errors in cases where multiple sites are hosted by the same server.