mod_cache: Fix parsing of quoted Cache-Control token arguments. PR 63288.

Make cache_strqtok() return both the token and its unquoted argument (if any),
or an error if the parsing fails.

Cache-Control integer values (max-age, max-stale, ...) can then be parsed w/o
taking care of the (optional) quoting.

Suggested by: fielding


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1856493 13f79535-47bb-0310-9956-ffa450edef68