This is very simple but thought i would share anyway because maybe it might help someone. 

When you set dev mode to true in your config file then you have to go back and set it back to false when you are done.  This opens the door for typos or worse maybe forgetting the ) or the ; or overwriting something. 

So here is a different way and less key strokes and lessor chance of typo.

Just make two entries.

      define('OW_DEV_MODE', false);
 //    define('OW_DEV_MODE', true);

notice how one of them is commented out with //  so all you have to do now to turn it on is to do this..

//  define('OW_DEV_MODE', false);
        define('OW_DEV_MODE', true);

so much easier to mess with doing // than to mess with the command itself.  Just remove the // from one and put it on the other, easy peasy...

hope that helps...  :)