- 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.

If we find a type that
- we think we can reason about statically
- does not have an __iter__ but can be iterated via __getitem__

we previously just bailed saying that we know it doesn't have an __iter__ method
(instead of calling getiterHelper like we should).  This bug exists on master as well,
but we just don't run into it that often (especially since it's llvm-tier-only).

With some prefetching.