Removing the alteration of Array.prototype with a custom function

When iterating over Array objects with a "for (propName in objectName)" syntax, this extra _indexOf method shows up.  While not a problem for most code, I have had problems with other plugins that iterate over Arrays without checking their length.

In addition to submitting pull requests to fix that other code, I'm also trying to help avoid the problems that this plugin might have with the rest of the world.