* Added GPU emitter for op::Result.
For now it simply copies the output tensor.

All but 3 tests now pass. The remaining
failing tests are:
* GPU.dot_0_0
* GPU.dot_matrix_2x0_0x2
* GPU.dot_2x0_0

* Removed call to handle memory aliasing in gpu_external_function.

* fix gpu emitter bug that will return in the middle of function

* Merge pull request #609 from NervanaSystems/tfl/fix_return_bug

fix gpu emitter bug that will return in the middle of function

* GPU backend skips added for recent softmax test and updated aliased output test that uses op::Constant.