[BUGFIX beta] Fix `DataAdapter#getModelTypes()` to return Ember.Array

IE8 doesn't have `Array#map` and `Array#filter`.
This PR fixes:
![__________2014-05-26_23 55 21](https://cloud.githubusercontent.com/assets/290782/3096380/55dec21a-e5d3-11e3-933e-917b818bbf82.png)

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And #4931, #4936 and this errors are resolved, all tests are passed on IE8.
![2014-05-28 4 11 20](https://cloud.githubusercontent.com/assets/290782/3096393/7ce9f690-e5d3-11e3-86f4-16d23c0e52ab.png)