Halide improvements

- Working interpolate example
- Clean up, comment bits of halidetuner.py
- Automatically allocate appropriately-sized output buffers in Halide test runner. This depends on Halide changes not yet pushed to master by @jrk
- Switch default compiler to c++ - tuner now works on OS X, not just Ubuntu.
- Track program version in tuner database.
- Fixes to allow multiple tuner instances to run concurrently.
- Save all broken schedules for later debugging.