Changed test to show JsonVisitorTest::testAddsJsonHeader fail
Changed test to show XMLVisitorTest::testSerializesXml fail
Fix JSON and XML request visitors to set Content-type before body
Removed guessing of request body content type by request path. Reverts part of 863998bb.
Merge pull request #414 from checat/adds-json-header-fail

Json and XML visitors do not set correct Content-type when path has known extension