[CXF-4846] A confusing excpetion may be thrown from HTTPConduit when oneway call results in HTTP 500 resp (only for 2.6.x)

git-svn-id: https://svn.apache.org/repos/asf/cxf/branches/2.6.x-fixes@1450509 13f79535-47bb-0310-9956-ffa450edef68