Allow mod_deflate to be more tolerant of multiple content-encodings.

- Tighten scope of a few affected variables (accepts, token).
- Look for gzip in r->headers_out (!) - if there, we've already compressed.
  (Previously, we'd look at r->headers_in which was bogus - we're output.)
- Switch the Accept-Encoding check to be case-insensitive per RFC 2616.
- Remove commented-out code.
- If C-E wasn't present or it was just "identity," set C-E to "gzip",
  otherwise, merge "gzip" onto the C-E list.

This patch was originally submitted by Ian and cleaned up and tested by
Justin.

Submitted by:	Ian Holsman
Reviewed by:	Justin Erenkrantz


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@95339 13f79535-47bb-0310-9956-ffa450edef68