Make differences detection in generated code report better
Make differences detection in generated code report better

Summary: Reverse the diff comparison so it shows the the difference from the current test fixture to the newly generated code (rather than the other way around)

Reviewed By: yfeldblum

Differential Revision: D27189542

fbshipit-source-id: dd04b3887605aea8f08c09e593bbe312f8089f46

facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift,facebook/fbthrift