Reimplement deflate_check_etag() so that it isn't such a pig

and correctly works with weak etags.  Related to PR 39727.

Note that there remains an error in ap_meets_conditions because
that function does not currently check for a transformed etag.
I am working on that.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@743595 13f79535-47bb-0310-9956-ffa450edef68