make Pool connection event emit just the connection and not an error, as pointed out by @dougwilson in issue #486

Author: marcuswestin

lib/Pool.js

@@ -43,7 +43,7 @@ Pool.prototype.getConnection = function (cb) {
         return cb(err);
       }
 
-      this.emit('connection', null, connection);
+      this.emit('connection', connection);
       return cb(null, connection);
     }.bind(this));
   }

test/integration/pool/test-connection-event.js

@@ -4,7 +4,7 @@ var Connection = require(common.lib + '/Connection');
 var pool       = common.createPool();
 
 var connectionEventHappened = false;
-pool.on('connection', function(err, connection) {
+pool.on('connection', function(connection) {
   connectionEventHappened = true;
 })