lfs: don't require the .hglfs file to be tracked to control the policy The .hgignore file doesn't need to be tracked, nor does the git equivalent of this file. I'm still a little concerned about the effects of forgetting to commit this file. But the fact that conversions maintain the hashes if only the normal vs external storage changes, should make this less risky.

tests: add a pattern to fix --pure tests Test Plan: ran all tests with and without --pure, everything passed on gcc112. Differential Revision: https://phab.mercurial-scm.org/D1946

streamclone: add a comment about non-publishing being broken with v1 This change was suggested by Gregory Szorc.

streamclone: move requirement update into consumev2 This change was suggested by Gregory Szorc.

streamclone: use readexactly when reading stream v2 Yuya Nishihara pointed out that it is safer.

streamclone: rename '_emit' to '_emit2' for clarity This change was suggested by Gregory Szorc.

help: do not suggest "update --clean ." to cancel uncommitted merge Follows up 41ef02ba329b.