as reported by Neal on python-dev.

Python 2.4 changed ntpath.abspath to do an import
inside the function.  As a result, due to Python's
import lock, anything calling abspath on Windows
(directly, or indirectly like tempfile.TemporaryFile)
hung when it was called from a thread spawned as a
side effect of importing a module.

This is a depressingly frequent problem, and
deserves a more general fix.  I'm settling for
a micro-fix here because this specific one accounts
for a report of Zope Corp's ZEO hanging on Windows,
and it was an odd way to change abspath to begin
with (ntpath needs a different implementation
depending on whether we're actually running on
Windows, and the _obvious_ way to arrange for that
is not to bury a possibly-failing import _inside_
the function).

Note that if/when other micro-fixes of this kind
get made, the new Lib/test/threaded_import_hangers.py
is a convenient place to add tests for them.

way to guarantee a deadlock on the next call!

If I've inadvertently done some damage to this test, sorry (but I don't
think I have).

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. :)

Fix exit races in test_thread.py and test_threaded_import.py.
I suspect the bug is provokable only under Linux (where child threads
seem to get lots of cycles before they get killed after the main thread
exits), or on multi-processor machines running other OSes.
Bugfix candidate.

when that test is doomed to deadlock.

in which case it will hang because the import lock is already held
by the main thread.

When regrtest.py finds an attribute "test_main" in a test it imports,
regrtest runs the test's test_main after the import.  test_threaded_import
needs this else the cross-thread import lock prevents it from making
progress.  Other tests can use this hack too, but I doubt it will ever be
popular.

ICK ALERT:  read the long comment block before run_the_test().  It was
almost impossible to get this to run without instant deadlock, and the
solution here sucks on several counts.  If you can dream up a better way,
let me know!