Add return statements for promises to fix Bluebird errors.

Fixes: neumino#285

lib/pool.js

@@ -96,7 +96,7 @@ Pool.prototype.getConnection = function() {
     }
 
     if (self._slowGrowth === false) {
-      self._expandBuffer();
+      return self._expandBuffer();
     }
 
   });
@@ -245,7 +245,7 @@ Pool.prototype.createConnection = function() {
 
       // Not sure what happened here, so let's be safe and close this connection.
       connection.close().then(function() {
-        self._expandBuffer();
+        return self._expandBuffer();
       }).error(function(e) {
         // We failed to close this connection, but we removed it from the pool... so err, let's just ignore that.
         self._expandBuffer();
@@ -318,7 +318,7 @@ Pool.prototype._expandBuffer = function() {
   if ((this._draining === false) &&
       (this._pool.getLength() < this.options.buffer+this._localhostToDrain) &&
       (this._numConnections < this.options.max+this._localhostToDrain)) {
-    this.createConnection();
+    return this.createConnection();
   }
 }