FELIX-4230 - Enhance SSL filter to forward client certificates:

- added some logging and exception handling to make sure that error
  situations are traceable;
- did some monkey tests on SSL certificate forwarding, which seems to
  work properly.



git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1542257 13f79535-47bb-0310-9956-ffa450edef68