added support to memcache for UNIX domain sockets

!empty evaluatues config param "port" with value "0" to false

see: http://www.php.net/manual/en/memcache.connect.php
"variable host: Point to the host where memcached is listening for connections. This parameter may also specify other transports like unix:///path/to/memcached.sock to use UNIX domain sockets, in this case port must also be set to 0."