reorganize mod_socache_redis so it compiles w/o apr-redis

It looks like this was the original intent. The provider
is not registered if apr-redis is missing.

It was previously failing to compile due to the dirconf being
hidden behind the #ifdef guard but not the routine module
code that used it.




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1769712 13f79535-47bb-0310-9956-ffa450edef68