Tweaks to compare_transform
Tweaks to compare_transform

Summary:
* Delete empty lines before diffing
* Pipe diff output straight to file instead of printing to console -- when
  diffing large APKs printing to the console locks up the remote session and
  is really annoying

Reviewed By: dariorussi

Differential Revision: D4409023

fbshipit-source-id: 5377cbb5b741ebe8a73299151d325c2c40693b18

facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex,facebook/redex