osutil: use Python memory allocator in _listdir The Python memory allocator has performance advantages for small allocations.

bdiff: use Python memory allocator in fixws Python has its own memory allocation APIs. For allocations <= 512 bytes, it allocates memory from arenas. This means that average small allocations don't call the system allocator, which makes them faster. Also, arena allocations cut down on memory fragmentation, which can matter for performance in long-running processes. Another advantage of using the Python memory allocator is that allocations are tracked by Python. This is a bigger deal in Python 3, as modern versions of Python have some decent built-in tools for examining memory usage, leaks, etc. This patch converts a trivial malloc() + free() in the bdiff code to use the Python allocator APIs. Since the object being operated on is a line, chances are it will use an arena. So, this could have a net positive impact on performance (although I didn't measure it).

localrepo: fix deprecation warning version of wfile The patch lingered a bit too long in my local clone and I messed up when I updated the version number. Since nobody caught it, I'm fixing the version after the fact.

util: explicitly tests for None Changeset 8b6927eb7efd removed the mutable default value, but did not explicitly tested for None. Such implicit checking can introduce semantic and performance issue. We move to an explicit check for None as recommended by PEP8: https://www.python.org/dev/peps/pep-0008/#programming-recommendations