Rewrote. As reported on c.l.py, when the test suite is run via

Rewrote.  As reported on c.l.py, when the test suite is run via
"import test.autotest", temp_imp failed because the import lock was
still held at the test's end (the test assumed it wouldn't be), and
then a RuntimeError got raised at the end of the entire suite run because
test_imp cleared the import lock as a side effect of trying to test that
the import lock wasn't held (but a legitimate import is in progress,
so the lock should be held, and the import machinery complained when it
found that the lock was unexpectedly cleareed).

Also removed the unittest scaffolding.  It didn't buy anything here, and
the test was raising regrtest's TestFailed instead of using the unittest
failure-reporting mechanisms.