docs: Clarify DPI flag wording re: PATH_INFO vs URL-path

docs: Clarify DPI flag wording re: PATH_INFO vs URL-path

The opening sentence of the DPI|discardpath section implied PATH_INFO
was a "portion of" the URL-path/URI, while the next sentence described
it as a separate value concatenated to the URL-path/URI. Reword to
make clear that PATH_INFO is appended, not an inherent component.

Also add glossary links for URL-path (trunk only).

bz#70052

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1934603 13f79535-47bb-0310-9956-ffa450edef68