From SF patch #852334.

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. :)

Tested for not breaking builds on Linux.

newlines at the start or end.  Fiddle test_popen2 and popen2._test() to
tolerate this.  Also change all "assert"s in these tests to raise
explicit exceptions, so that python -O doesn't render them useless.
Also, in case of error, make the msg display the reprs of what we
wrote and what we read, so we can tell exactly why it's failing.

   but no os.fork