Session cache interface redesign, Part 8:

Abstract out the mod_ssl session caching interface into a separate set
of modules, mod_socache_*.

* modules/cache/ap_socache.h: New file.

* modules/cache/config.m4: Copy CHECK_DISTCACHE from ../ssl/config.m4; 
  add new socache modules.

* modules/cache/mod_socache_dbm.c: Copied from ../ssl/ssl_scache_dbm.c.
  s/ssl_scache_/socache_/; add module structure and register_hooks.

* modules/cache/mod_socache_shmcb.c: Copied from ../ssl/ssl_scache_shmcb.c.
  s/ssl_scache_/socache_/; add module structure and register_hooks.
  Add SHMCB_MAX_SIZE definition, replacing APR_SHM_MAXSIZE.

* modules/cache/mod_socache_memcache.c: Copied from
  ../ssl/ssl_scache_memcache.c.
  s/ssl_scache_/socache_/; add module structure and register_hooks.
  Enable for APR-Util 1.3.x at compile-time, omitting configure-time
  checks.

* modules/cache/mod_socache_dc.c: Copied from ../ssl/ssl_scache_dc.c.
  s/ssl_scache_/socache_/; add module structure and register_hooks.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@645844 13f79535-47bb-0310-9956-ffa450edef68