'key' property breaks mustache helpers

Any time an object passed via a mustache template to a helper contains a "key" property, the scope is not passed correctly (probably also true if the object has an "index" or "value" property).

Seems to be due to https://github.com/bitovi/canjs/blob/master/view/mustache/mustache.js#L71.

@imjoshdean looks like its because of the new directives you added to mustache?  Can you please take a look?

This test passes in v2.0.0 but fails in v2.0.1