Use one variable assignment per declaration.

I am working through a code style cleanup effort using [jscs](https://github.com/mdevils/node-jscs) rules. 

You can see the script and rules in: https://github.com/rwjblue/ember.js/compare/code-style-rules

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This applies the `disallowMultipleVarDeclWithAssignment` rule to `ember-metal`.