Add PATH_INFO glossary entry, link first mention in each doc

Add PATH_INFO glossary entry, link first mention in each doc

Define PATH_INFO in glossary.xml with an example
(/app/index.php/extra/path), reference to AcceptPathInfo directive,
and RFC 3875 section 4.1.5 citation.

Convert the first prose mention of PATH_INFO in 14 files to
<glossary ref="pathinfo"> links. Subsequent mentions within the same
document are left as <code> or plain text to avoid link spam.

Skipped mod_ext_filter.xml (only occurrence is inside the compound
variable name DOCUMENT_PATH_INFO) and mod_ssl.xml (inside a <pre>
block where markup links are inappropriate).

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1934245 13f79535-47bb-0310-9956-ffa450edef68