Incomplete patch.  Would be great if someone picked
this up and ran with it.  Need to be conservative and
try not to use too much memory in these tests.

Should start with strings and unicode.  Those will be
the most important things to test first.  Then can move
to arrays, mmap and other sequences.  Eventually on to
lists, sets, and dicts.

Right now, I'm sticking this in
Lib/tests/bigmem/test_str.py.