See there for a description.
Added test case.
Bugfix candidate for 2.2.x, not sure about previous versions:
probably low priority, because virtually no one runs debug builds.
imports e.g. test_support must do so using an absolute package name
such as "import test.test_support" or "from test import test_support".
This also updates the README in Lib/test, and gets rid of the
duplicate data dirctory in Lib/test/data (replaced by
Lib/email/test/data).
Now Tim and Jack can have at it. :)