v6.37.0. Improvement.

- v6.37.0 May 29, 2013
	- Plugin tester file is now optional when specifying something like
`testerClass: 'RendererTester'` inside your plugin test file
		- Closes [issue #487](https://github.com/bevry/docpad/issues/487)
	- `enableUnlistedPlugins` is now set to `true` when running plugin
tests (it was `false` before)
		- This allows us to remove the need for the plugin tester file for
most situations