filemerge: remove unused `orig` argument from tool functions Differential Revision: https://phab.mercurial-scm.org/D11878

filemerge: stop passing around 3 unused `None` values in `files` argument Since 67cfffbfb6a0 (filemerge: eliminate most uses of tempfiles, 2017-08-31), we have used only the last entry in the `files` tuple that gets passed around to various functions. That commit said "Emphasize that they're unused so we can more easily remove them later.". It's now "later". Differential Revision: https://phab.mercurial-scm.org/D11877

filemerge: rename backup variables from `back` to `backup` `backup` seems like an obviously clearer name for something containing something related to a backup. Differential Revision: https://phab.mercurial-scm.org/D11876

setup.py: fix some documentation typos Differential Revision: https://phab.mercurial-scm.org/D11944

dirstate-v2: Apply SECOND_AMBIGUOUS to directory mtimes too This would only be relevant in contrived scenarios such as a dirstate file being written with a libc that supports sub-second precision in mtimes, then transfered (at the filesystem level, not `hg clone`) to another system where libc *doesn’t* have sub-second precision and truncates the stored mtime of a directory to integer seconds. Differential Revision: https://phab.mercurial-scm.org/D11939

rank: actually persist revision's rank in changelog-v2 The changelog v2 format is now persisting whatever "rank" value is recorded. However keep in mind that for we do not record any value. Differential Revision: https://phab.mercurial-scm.org/D11937