branchmap: stringify int in a portable way We actually need a bytes in Python 3, and thanks to our nasty source loader this will portably do the right thing.

branchmap: don't use buffer() on Python 3 This is certainly slower than the Python 2 code, but it works, and we can revisit it later if it's a problem.

py3: use bytearray() instead of array('c', ...) constructions Portable from 2.6-3.6.