Added server_timeout_counter and behavior MEMCACHED_BEHAVIOR_SERVER_TIMEOUT_LIMIT.

Added server_timeout_counter and behavior MEMCACHED_BEHAVIOR_SERVER_TIMEOUT_LIMIT.

This feature works as follows:
When a timeout occurs, retry MEMCACHED_BEHAVIOR_SERVER_TIMEOUT_LIMIT times before
putting the server in MEMCACHED_SERVER_STATE_IN_TIMEOUT state.

It makes sense to not fail from the 1st time but retry on the next calls before marking
the server as timeout.