Add debug output to result about bats

[JohannesFKnauf]

Recently we wanted to conveniently enable debug out of the full output of run commands in tests. We did not find a really satisfying solution, but stumpled upon this issue immediately. So adding for all the lost souls with the same problem:

We worked around it by adding some debug code to the teardown() { } function, which has all necessary variables in scope.

[sstephenson]

Bats will now tell you the test filename and line number that triggers the failure: bc72b85