binary deletes were not ticking stats counters

Thanks to Stephen Yang for the bug report.

memcached.c

@@ -2159,6 +2159,9 @@ static void process_bin_delete(conn *c) {
         uint64_t cas = ntohll(req->message.header.request.cas);
         if (cas == 0 || cas == ITEM_get_cas(it)) {
             MEMCACHED_COMMAND_DELETE(c->sfd, ITEM_key(it), it->nkey);
+            pthread_mutex_lock(&c->thread->stats.mutex);
+            c->thread->stats.slab_stats[it->slabs_clsid].delete_hits++;
+            pthread_mutex_unlock(&c->thread->stats.mutex);
             item_unlink(it);
             write_bin_response(c, NULL, 0, 0, 0);
         } else {
@@ -2167,6 +2170,9 @@ static void process_bin_delete(conn *c) {
         item_remove(it);      /* release our reference */
     } else {
         write_bin_error(c, PROTOCOL_BINARY_RESPONSE_KEY_ENOENT, 0);
+        pthread_mutex_lock(&c->thread->stats.mutex);
+        c->thread->stats.delete_misses++;
+        pthread_mutex_unlock(&c->thread->stats.mutex);
     }
 }