TableProcessor.endRow should restore resevedAtBottom on the right context

This pull fix a bug that causes `TableProcessor.endRow()` to miscalculates the available height when the `dontBreakRows` is set to `true`. [**plunker example**](http://plnkr.co/edit/ZQjyJ5v2WSt6vbhIBbcm?p=preview)


![image](https://cloud.githubusercontent.com/assets/5453835/4269575/2e6631d6-3cbe-11e4-99ea-c537d3223f15.png)


when `dontBreakRows` is set the space is reserved in the nested `DocumentContext`  (created by `beginUnbreakableBlock()` ) and restored on the top context (because `commitUnbreakableBlock()` is called before the space is restaured).