share deaduntils between hosts

This will help avoid many socket timeout especially when we use
python-memcached with eventlet.

For example,When use eventlet,for each greenlet we call client.get
first time,the client will be rebuild,and client.servers[*].deaduntil
will be 0.For each http request,we will have one greenlet.So we get
a socket timeout for each request.
This could be fixed in application,but i believe it's better to fix
it in python-memcached.

memcache.py

@@ -1330,6 +1330,9 @@ def check_key(self, key, key_extra_len=0):
                 "Control/space characters not allowed (key=%r)" % key)
 
 
+_host_last_deaduntils = {}
+
+
 class _Host(object):
 
     def __init__(self, host, debug=0, dead_retry=_DEAD_RETRY,
@@ -1371,7 +1374,7 @@ def __init__(self, host, debug=0, dead_retry=_DEAD_RETRY,
             self.port = int(hostData.get('port') or 11211)
             self.address = (self.ip, self.port)
 
-        self.deaduntil = 0
+        self.deaduntil = _host_last_deaduntils.get(self.ip, 0)
         self.socket = None
         self.flush_on_next_connect = 0
 
@@ -1411,6 +1414,7 @@ def _get_socket(self):
             s.connect(self.address)
         except socket.timeout as msg:
             self.mark_dead("connect: %s" % msg)
+            _host_last_deaduntils[self.ip] = self.deaduntil
             return None
         except socket.error as msg:
             if isinstance(msg, tuple):