Extend expression parser registration to support

ssl variables in any expression using
mod_rewrite syntax "%{SSL:VARNAME}" or function
syntax "ssl(VARNAME)".

Backport of r1707002 and r1709596 from trunk.

Committed By: rjung
Backported By: rjung
Reviewed by: rjung, ylavic, sf


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1710433 13f79535-47bb-0310-9956-ffa450edef68