sparse: move code for importing rules from files into core This is a pretty straightforward port. Some code cleanup was performed. But no major changes to the logic were made. I'm not a huge fan of this function because it does multiple things. I'd like to get things into core first to facilitate refactoring later. Please also note the added inline comment about the oddities of writeconfig() and the try..except to undo it. This is because of the hackiness in which the sparse matcher is obtained by various consumers, notably dirstate. We'll need a massive refactor to address this. That refactor is effectively blocked on having the sparse dirstate hacks live in core.

sparse: refactor activeprofiles into a generic function (API) activeprofiles() is a special case of a more generic function. Furthermore, that generic function is essentially already implemented inline in the sparse extension. So, refactor activeprofiles() to a generic activeconfig(). Change the only consumer of activeprofiles() to use it. And have the inline implementation in the sparse extension use it.

check-code: prohibit `if False` antipattern Differential Revision: https://phab.mercurial-scm.org/D20

convert: remove `if False` block This code has never run since its introduction on July 18th, 2007. It's time for it to go. Differential Revision: https://phab.mercurial-scm.org/D19

filterpyflakes: move self-test into test file This will avoid a false positive on an upcoming check-code rule. Differential Revision: https://phab.mercurial-scm.org/D18

test-subrepo: demonstrate a status problem when merge deletes a file At the interactive update prompt, if (c) is chosen and then followed by `hg rm`, both `status -R` and `status -S` show the file as 'R', and `files -R` shows no files (OK, because explicitly removed files aren't supposed to be listed). If `rm` follows selecting (c), then both flavors of `status` list the file as '!', and `files -R` lists the missing file. So somehow, the (d) option has followed a third path.

subrepo: make the output references to subrepositories consistent Well, mostly. The annotation on subrepo functions tacks on a parenthetical to the abort message, which seems reasonable for a generic mechanism. But now all messages consistently spell out 'subrepository', and double quote the name of the repo. I noticed the inconsistency in the change for the last commit.

subrepo: consider the parent repo dirty when a file is missing This simply passes the 'missing' argument down from the context of the parent repo, so the same rules apply. subrepo.bailifchanged() is hardcoded to care about missing files, because cmdutil.bailifchanged() is too. In the end, it looks like this addresses inconsistencies with 'archive', 'identify', blackbox logs, 'merge', and 'update --check'. I wasn't sure how to implement this in git, so that's left for someone more familiar with it.