mod_rewrite, mod_proxy: mod_proxy to cononicalize rewritten [P] URLs. PR 69235.

mod_rewrite, mod_proxy: mod_proxy to cononicalize rewritten [P] URLs. PR 69235.

When mod_rewrite sets a "proxy:" URL with [P], it should be canonicalized by
mod_proxy still, notably to handle any "unix:" local socket part.

To avoid double encoding in perdir context, a follow up commit should remove the
ap_escape_uri() done in mod_rewrite since it's now on mod_proxy to canonicalize,
per PR 69260.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1920570 13f79535-47bb-0310-9956-ffa450edef68