test_cleanup: use int32 instead of uint32

If an int32 is interpreted as unsigned, then the code should have no
problem accepting negative numbers. They're bits, after all.

This isn't the case for types such as int8 or int16, which are in fact
int32s. A negative int32 is defintely not an int8.
test_cleanup: use proper False constant in _oasis

false is not the same as False. This may have been the cause for #7.
Merge pull request #8 from frenetic-lang/test_cleanup

_oasis is sort of bad.