CLN: Better exceptions and tests for core/frame
CLN: test_frame fixups + core/frame improvements
CLN: Big simplification of test_frame
ENH: Have assertRaises maintain traceback

* Adds `raise_with_traceback` to `pandas.compat`, which handles the
  Python 2/3 syntax differences for raising with traceback.
* Uses `raise_with_traceback` in `assertRaises` and `assertRaisesRegexp`
  so they provide better feedback.
TST: Test shape mismatch for dot product.
small assertRaisesRegexp fixups
more minor fixups
fixup! more minor fixups
TST: Test cases for bad input exceptions to to_timestamp
remove an assert False (cuz its now tested