lfs: avoid an improper usage of os.path.basename() to parse a URI

lfs: add an experimental knob to disable blob serving The use case here is the server admin may want to store the blobs elsewhere. As it stands now, the `lfs.url` config on the client side is all that enforces this (the web.allow-* permissions aren't able to block LFS blobs without also blocking normal hg traffic). The real solution to this is to implement the 'verify' action on the client and server, but that's not a near term goal. Whether this is useful in its own right, and should be promoted out of experimental at some point is TBD. Since the other two tests that deal with LFS and `hg serve` are already complex and have #testcases, this seems like a good time to start a new test dedicated to access checks against the server. Instead of conditionally wrapping the wire protocol handler, I put this in the handler because I'd still like to bring the annotations in from the evolve extension in order to set up the wrapping. The 400 status probably isn't great, but that's what it would be for existing `hg serve` instances without support for serving blobs.

stringutil: edit comment to reflect actual data type name In development the data type used to hold an email/name pair was called a "mailmaptup" since it was implemented as a namedtuple. The implementation has since been changed to use an @attr.s decorated class named mailmapping. This commit changes a comment to reflect this change. Differential Revision: https://phab.mercurial-scm.org/D3004

stringutil: improve check for failed mailmap line parsing The existing check for a bad mailmap file entry fails with inputs like b'>@<'. This commit adds a function to check if a sufficient amount of information has been parsed from a mailmap file entry. At minimum, one email must be found (assumed to be the commit email). If email is not empty and no names are found, then there must be two emails. If there are at least one email and name, the mapping is valid. Differential Revision: https://phab.mercurial-scm.org/D3003

stringutil: rename local email/names variables to their plural forms email and name variables are renamed to emails and names (respectively). This is because the email variable name shadows the email function within the stringutil module. Since we are renaming email, we also rename name for consistency. Differential Revision: https://phab.mercurial-scm.org/D3002

templatefuncs: remove redundant "or author" from mailmap return statement Differential Revision: https://phab.mercurial-scm.org/D3001

lfs: add the 'Content-Type' header called out in the file transfer spec https://github.com/git-lfs/git-lfs/blob/master/docs/api/basic-transfers.md#uploads

lfs: improve the client message when the server signals an object error Two things here. First, the previous message included a snippet of JSON, which tends to be long (and in the case of lfs-test-server, has no error message). Instead, give a concise message where possible, and leave the JSON to a debug output. Second, the server can signal issues other than a missing individual file. This change shows a corrupt file, but I'm debating letting the corrupt file get downloaded, because 1) the error code doesn't really fit, and 2) having it locally makes forensics easier. Maybe need a config knob for that.