osutil: implement pure version of recvfds() for PyPy This is less portable than the C version, but PyPy can't load CPython extensions. So for now, this will be used on PyPy. I've tested it on Linux amd64 and Mac OS X.

osutil: implement recvmsg() of SCM_RIGHTS for chg command server It will be used to attach client's stdio files to a background chg command server. The socket module of Python 2.x doesn't provide recvmsg(). This could be implemented by using ctypes, but it would be less portable than the C version because the handling of socket ancillary data heavily depends on preprocessor. Also, some length fields are wrongly typed in the Linux kernel.

cleanup: back out performance hacks amended into previous commit

commands: consistently indent notes 3 spaces most notes have 3 spaces for indentation, these had 2...

perf: add perfrevlogrevision As part of investigating performance improvements to revlog reading, I needed a mechanism to measure every part of revlog reading so I knew where time was spent and how effective optimizations were. This patch implements a perf command for benchmarking the various stages of reading a single revlog revision. When executed against a manifest revision at the end of a 30,000+ long delta chain in mozilla-central, the command demonstrates that ~80% of time is spent in zlib decompression.

commands: use revlog._deltachain in debugdeltachain We have a nice API now. Use it. This does mean we introduce an extra index lookup for each revision. Considering this is a debug command, the overhead should be acceptable. We could add the chain size to revlog._deltachain(). However, that feels like avoidable overhead.

revlog: refactor delta chain computation into own function This code is already written in multiple locations. While this code needs to be fast and extracting it to its own function adds overhead, code paths reading delta chains typically read, decompress, and do binary patching on revlog data from the delta chain. This other work (especially zlib decompression) almost certainly accounts for a lot more time than the overhead of introducing a Python function call. So I'm not worried about the performance impact of this change.