Turn off the 'dangling-thread' test since it's not reliable in CPython

And turn off that part of the fork.py test as well
Have to set CCACHE_CPP2=yes to work around some clang+ccache issues
Import a bunch more CPython code to get str.format() working

Starting to really hit critical mass in terms of having enough
API support that it's easier to copy additional API functions over.
Merge branch 'str.format'
[HAX] not addressing these for now