mod_rewrite: Fix UDS ("unix:") scheme for [P] rules.  PR 57691 + 65590.

Handle the unix: scheme as an obsolute URI or a rule like:
  RewriteRule ^/(.*) unix:/path/to/uds.sock|fcgi://localhost/$1 [P]
sets r->filename for /index.html as:
  proxy:http://www.example.com/unix:/path/to/uds.sock|http://localhost/index.html
instead of the expected:
  proxy:unix:/path/to/uds.sock|http://localhost/index.html

Submitted by: Janne Peltonen <janne.peltonen sange.fi>
Reviewed by: ylavic



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1893516 13f79535-47bb-0310-9956-ffa450edef68
