FELIX-3988 - better handling of HttpContext#handleSecurity:

- in case the HttpContext#handleSecurity either committed its own
  response, or did set a non-default status code, do not overwrite
  the status code with SC_FORBIDDEN;
- modified logic for both the FilterHandler & ServletHandler to make
  them symmetrical, added additional test cases to verify the 
  behaviour.



git-svn-id: https://svn.apache.org/repos/asf/felix/trunk@1567863 13f79535-47bb-0310-9956-ffa450edef68