Comment 3 for bug 926869

This seems to be testing gc-dependent behaviour of tests warning if
they're not collected. The behaviour is obviously going to be
different on pypy (and other Python implementations), so I would be ok
with just making it skip if it's not cpython. gz might feel
differently.

If we suspect there is test infrastructure accumulating in memory when
running under pypy we might need to work out some other way to test
for that.