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.

py3: byteify the decoded JSON responses upon receipt in the LFS blobstore It got too confusing juggling r'' vs b'' across several functions.

hgweb: ensure Content-Length and Content-Type are not promoted to HTTP_ on py3 In stabilizing test-lfs-serve-access.t for py3, the server started asserting on blob upload: Environment should not have the key: HTTP_CONTENT_LENGTH (use CONTENT_LENGTH instead) It could be avoided by explicitly setting the Content-Length header on the client side. I didn't go back to py2, but printing the original header here in py37 revealed 'Content-length' when sent to the error log.

py3: raw stringify various JSON and HTTP headers in the LFS blobstore module This is (almost?) entirely from Augie's work. I'm a bit surprised that the JSON data is being encoded with ASCII via `pycompat.bytesurl()`- I would have thought UTF-8.