- change up interpreter-shutdown to better deal with objects with custom finalizers
- fix a bunch of mixed decrefs for oldstyle-classes
- a couple other misc things

file.py is now working

I guess a number of tests do this to help with testing

instead of re-calculating it for every BB

profiling ftw

Don't use ValueMap::operator[], since that is much more
expensive than lookup().

I think `make check_dbg` is clean again.

Most of these need to return borrowed references in order to match the C API.