Provie a mechanism to specify cache type from NONE, APC, or MEMCACHE
based on a config variable.

If MEMCACHE type is selected, a list of servers can be specified to
provide multiserver support. Note that php-memcaced is required for
MEMCACHE support.

Lukas: Minor commenting style fixes.

Signed-off-by: Lukas Fleischer <archlinux@cryptocrack.de>