Do not do get of null

If you try 'get(null, "length")' in the console you will see that it returns 3 (!?). If you happen to have 3 elements in the content initially, it fails later on.
Merge pull request #272 from juggy/patch-1

Do not do get of null
Return promises from RecordArray#reload.
Merge pull request #279 from karenliu1/karen/return-from-record-array

Return promises from RecordArray#reload.
Reset dirty attributes on Model#reload.
Merge pull request #280 from karenliu1/reload-dirty-tracking

Reset dirty attributes on Model#reload.
fixes for ember debug adapter
Merge pull request #281 from mreinsch/fix-debug-adapter

fixes for ember debug adapter