Fix for multiple proxy bugs - review please:

Fix for multiple proxy bugs - review please:

#10722  Reverse proxying cookies
#15207  Proxy passing canonicalised URIs to backend
#16812  Case-insensitivity of proxypassreverse
#19317  Canonicalised URI causing infinite loop
#20372  AllowEncodedSlashes
May also fix 13577 (untested)

This is really two fixes: 10722 and 15207; the others are trivial consequences.
To make review easier, the simpler fix (#15207) is entirely contained in
#ifdef FIX_15207 (new code) and
#ifndef FIX_15207 (removed code)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104070 13f79535-47bb-0310-9956-ffa450edef68