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.

py3: byteify the LFS blobstore module This is almost entirely b'' prefixing, with a couple of exceptions forced to bytes. Much of this is also borrowed from Augie's code. There's an HTTPError.read() that I flagged that I assume needs to be converted to bytes, but I can't find confirmation. Handling the deserialized JSON object over several functions made r'' vs b'' accesses confusing, so this assumes that the JSON object will be converted to bytes immediately. That will be done in the following commits, so it's not buried in these trivial changes.

py3: raw stringify various things in the LFS server module Some of this is based on code written by Augie. I'm slightly unsure if these are the correct pycompat bytes <-> str conversion methods.

py3: add b'' prefixes to the LFS server module There are a ton of these changes in the blobstore, as well as r'' prefixing. So separating these out hopefully makes review easier. # skip-blame for b'' prefixing

py3: add b'' and r'' prefixes to LFS tests

py3: more tests from the ratchet Differential Revision: https://phab.mercurial-scm.org/D5730

dispatch: unify handler of IOError and OSError These exceptions were merged in Python 3.

dispatch: quote filename in IOError as well It's explicitly added for OSError at 720308f741cb "dispatch: show empty filename in OSError aborts". Let's do the same for IOError.