+ http: Support access to the original (unparsed) URI if available

New 'raw' field on Uri, set to the original raw data when parsing from a String or Byte Array. (This is not decoded or normalised in any way.)
If the the Uri was not parsed, the value is the same as toString().
= can: Test that requests from spray-can support access to the raw unparsed URI supplied by the client.
= servlet: Update the servlet request converter to set Uri.raw to the undecoded URI from the servlet container.