discovery import errors provide no useful information

[David Kranz]

If 'testr list-tests' gets an error it just tells you which test module failed. Many times if you import that module into the interpreter there will be no error. But if you run nose, it gives you a stacktrace that points you right at the problem.

[Robert Collins (lifeless)]

This is due to upstream python - see https://github.com/testing-cabal/testtools/pull/77 in testtools and upstream Python http://bugs.python.org/issue19746 - its not a testrepository issue (and testrepository, since the rendering of enumeration errors was fixed, will DTRT once the worker layer stuff is fixed.