Boost up performance for redis PUB-SUB patterns matching

If lots of clients PSUBSCRIBE to same patterns, multiple pattens matching will take place. This commit change it into just one single pattern matching by using a `dict *` to store the unique pattern and which clients subscribe to it.

src/server.c

@@ -1900,6 +1900,7 @@ void initServer(void) {
     evictionPoolAlloc(); /* Initialize the LRU keys pool. */
     server.pubsub_channels = dictCreate(&keylistDictType,NULL);
     server.pubsub_patterns = listCreate();
+    server.pubsub_patterns_dict = dictCreate(&keylistDictType,NULL);
     listSetFreeMethod(server.pubsub_patterns,freePubsubPattern);
     listSetMatchMethod(server.pubsub_patterns,listMatchPubsubPattern);
     server.cronloops = 0;