mod_rewrite: Better question mark tracking to avoid UnsafeAllow3F. PR 69197.

mod_rewrite: Better question mark tracking to avoid UnsafeAllow3F.  PR 69197.

Track in do_expand() whether a '?' in the uri-path comes from a literal in
the substitution string or from an expansion (variable, lookup, ...).
In the former case it's safe to assume that it's the query-string separator
but for the other case it's not (could be a decoded %3f from r->uri).

This allows to avoid [UnsafeAllow3F] for most cases.

Merges r1919325 from trunk
Reviewed by: ylavic, covener, jorton
Github: closes #462

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1919545 13f79535-47bb-0310-9956-ffa450edef68