pubsub: Return integers for NUMSUB, not strings

Also adds test for numsub — due to tcl being tcl,
it doesn't capture the "numberness" of the fix,
but now we at least have one test case for numsub.

Closes #1561

src/pubsub.c

@@ -358,7 +358,7 @@ void pubsubCommand(redisClient *c) {
             list *l = dictFetchValue(server.pubsub_channels,c->argv[j]);
 
             addReplyBulk(c,c->argv[j]);
-            addReplyBulkLongLong(c,l ? listLength(l) : 0);
+            addReplyLongLong(c,l ? listLength(l) : 0);
         }
     } else if (!strcasecmp(c->argv[1]->ptr,"numpat") && c->argc == 2) {
         /* PUBSUB NUMPAT */

tests/unit/pubsub.tcl

@@ -196,6 +196,10 @@ start_server {tags {"pubsub"}} {
         $rd1 close
     }
 
+    test "NUMSUB returns numbers, not strings (#1561)" {
+        r pubsub numsub abc def
+    } {abc 0 def 0}
+
     test "Mix SUBSCRIBE and PSUBSCRIBE" {
         set rd1 [redis_deferring_client]
         assert_equal {1} [subscribe $rd1 {foo.bar}]