add conf for range and failover
add range distribution
implement range distribution
add failover pool
use pool name as hash string prefix
add backup request
revise server health check
fix the assertion error when connection refused
handle cases when msg->owner == NULL
add probe related confs
add probe handlers and implement probe request
hook memcache stat update into response parser
add array_reset
add stats keys and vals array to message
add proto specific stats field to server
add memcache probe response handling code
add cold stats check code
fix some compilation warnings
make auto_probe_hosts configurable
auto connect to servers when auto_probe_hosts enabled