* modules/cache/ap_socache.h: Add ap_socache_instance_t object type.

* modules/cache/ap_socache.h: Add ap_socache_instance_t object type.
  Adjust the provider interface to use this instance type throughout.

* modules/cache/mod_socache_dbm.c,
  modules/cache/mod_socache_memcache.c,
  modules/cache/mod_socache_shmcb.c,
  modules/cache/mod_socache_dc.c: Adjust all implementations to
  define the instance object in place of the "struct context", and
  to take this object directly in the provider interface.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@645924 13f79535-47bb-0310-9956-ffa450edef68