Removing hop-by-hop headers for ProxyServlet

Motivation:
RFC 2616 specifies a number of headers that are hop-by-hop and proxy
server are required to remove them [1].

The issue I ran into was when the ProxyServlet was deployed on EAP 6.3
and the proxy server set the response header 'Transfer-Encoding: chunked'
which cause the client to fail as the response from the proxy was not
chunked.

Modifications:
Added a check of header names before adding them to them to the
HttpServletRequest.

[1] http://tools.ietf.org/html/rfc2616#section-13.5.1