Update php_memcached.c

Fixed compilation with libmemcached 1.0.8.
The symbols memcached_server_major_version, memcached_server_minor_version, memcached_server_micro_version have been introduced in libmemcached 1.0.9, not 1.0.9.
I checked the libmemcached sources here:
https://launchpad.net/libmemcached/+download