perf: add some documentation to perfindex It seems useful to document how the arguments can affect the benchmark.

perf: move cache clearing in the `setup` step of `perfheads` The cache clearing is pretty fast, but this seems more "correct".

revlog: document cext oddities in terms of object/caches This clarify why we just call clearcaches on a single object.

perf: document perfheads

py3: stabilize the output of lfs commandserver tests The print() statements were being output at the very end, so write to the same stdout sink as runcommand, and explicitly flush.

py3: conditionalize some LFS test output I'm not sure why the one stackframe is py2 only, but that seems harmless. The remaining failure is LfsCorruptionError printing the fully qualified name, as well as b'' around its message.

lfs: strip the response headers from the Batch API before printing For reasons unknown, py3 is adding an extra '\n' before the headers print out. This makes the output the same as py2.

py3: force hgweb.server error log to internally write unicode Otherwise, there's a lot of py2/py3 divergence in the LFS tests because of the "HG error" lines picking up a b'' prefix. wsgicgi.py uses procutil.stderr, so I assume the input was meant to be bytes.