Summary:
@public
Fixes [#393](https://github.com/facebook/react-native/issues/393). Currently the transformer assumes line-preserving compilers and defaults to a super-fast source map generation process. However, we need to support compilers that aren't preserving lines.
I had feared this wuold slow down the server but I came about a little known peace of the spec that defines an "indexed source map" just for the purpose of concating files: https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit
Test Plan:
1. runJestTests.sh
2. run server and click around example apps
3. add a custom transporter like babel
4. add a custom file and a debugger statement
5. debug in chrome and make sure it works
redbox still works
