Merge r1531961 from trunk:

Support optional initialization arguments for socache providers in
mod_authn_socache.

Submitted by: chrisd
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1540312 13f79535-47bb-0310-9956-ffa450edef68