socache API tweaks based on chrisd's review:

* include/ap_socache.h (ap_socache_provider_t::store): Take a pool.
  (ap_socache_provider_t::retrieve): Guarantee APR_NOTFOUND for a
  "not found" result.
  (ap_socache_provider_t::remove): Return an apr_status_t.

* modules/cache/mod_socache_dc.c, modules/cache/mod_socache_dbm.c,
  modules/cache/mod_socache_shmcb,
  modules/cache/mod_socache_memcache.c: Adjust accordingly.

* modules/ssl/ssl_scache.c (ssl_scache_store): Pass pool to
  sesscache->store.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@726059 13f79535-47bb-0310-9956-ffa450edef68