Runtest

This pull request:
- Fixes a warning with clang on new error handling code
- Moves some serious errors/exceptions from 'cout' to 'cerr' where they should be
- RunTests: Shows user vw stderr in case vw exits with non zero status
- RunTests: Adds some debugging (-v 4 optional at runtime) to RunTests

Apologies for the noise of adding and reverting platform.h, I just started moving to pull requests from branches and this was already in my master branch and tree.