use more intuitive variable names

ap_sub_req_*_uri  to use new_uri
ap_sub_req_*_file to use new_file
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git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@104757 13f79535-47bb-0310-9956-ffa450edef68