memcached_server_by_key actually returns a memcached_server_instance_st instead
of memcached_server_st. The structures were compatible to eachother, but this
recently changed between 1.0.5 and 1.0.13.

See https://bugs.launchpad.net/libmemcached/+bug/1076048 for more info.
Added 4 functions to further debug issues and error codes in a multi-server environment:

	getLastErrorMessage()
	getLastErrorCode()
	getLastErrorErrno()
	getLastDisconnectedServer()
Added MEMCACHED_BEHAVIOR_DEAD_TIMEOUT class constant 'OPT_DEAD_TIMEOUT' (new in 1.0.3)
Merge pull request #42 from poison/master

Fixed getServerByKey function