added an async_set command

added an async_set command

this socket channel can only be used for sending messages.
if the user tries to run any command which handles the response
MemcachedClient will raise an assert because opaque numbers dont
match anymore

Change-Id: I848e2e19fefab60c7e41a9561bf9ee773bf56af8

lib/mc_bin_client.py

@@ -133,6 +133,12 @@ def set(self, key, exp, flags, val):
         """Set a value in the memcached server."""
         return self._mutate(memcacheConstants.CMD_SET, key, exp, flags, 0, val)
 
+    def send_set(self, key, exp, flags, val):
+        """Set a value in the memcached server without handling the response"""
+        self.vbucketId = crc32.crc32_hash(key) & 1023
+        opaque = self.r.randint(0, 2 ** 32)
+        self._sendCmd(memcacheConstants.CMD_SET, key, val, opaque, struct.pack(SET_PKT_FMT, flags, exp), 0)
+
     def add(self, key, exp, flags, val):
         """Add a value in the memcached server iff it doesn't already exist."""
         return self._mutate(memcacheConstants.CMD_ADD, key, exp, flags, 0, val)