Handle exceptions in bdd hooks.

Without this an exception in a before hook (for example) would cause tests to hang.
Remove debugging info.
Improve exception handling for before/after hooks.

* Respect QUnit's notrycatch setting.
* Provide more information about what failed.
* Add tests for the exception handling.
Merge branch 'pr/13'

* pr/13:
  Improve exception handling for before/after hooks.
  Remove debugging info.
  Handle exceptions in bdd hooks.