HttpComponentsMessageSender inintuitive constructor

HttpComponentsMessageSender has two constructors, with and without
HttpClient, and the one with HttpClient omits adding a
SoapRemoveHeaderInterceptor.

This breaks in org.apache.http.protocol.RequestContent with new
ProtocolException("Content-Length header already present"), but only in
some containers (oc4j) and not in others (jetty, eclipe); this makes the
issue hard to debug.

Adding a note to the javadoc would help the developer pick the proper
constructor to avoid this issue.

Issue: SWS-835
Merge pull request #5 from ekonijn/master

* http_components_constructor:
  HttpComponentsMessageSender inintuitive constructor