notify: optional mail threading based on obsmarker When notify.reply is set and a changeset has a predecessor in the repository, include In-Reply-To pointing to the message-id that would have been generated for the oldest predecessor. This allows mail threading like Phabricator for common cases like rebasing changes, but will be optimal for cases like folding. Differential Revision: https://phab.mercurial-scm.org/D8172

pathutil: document that dirs map type implies manifest/dirstate processing

git: pass a list to pathutil.dirs to indicate that it is a manifest The python implementation of pathutil.dirs just uses a for loop which happens to work the same on both dicts and lists. The rust implementation actually figures out which of the two types it is, and directs the execution to either dirstate or manifest processing.

git: implement basic bookmark activation This is very limited, but it allows 'hg update foo' when already on foo. The caching is based on bmstore's caching.

git: implement a basic checkconflict bookmark store method It is heavily based on bmstore's own checkconflict.

git: abort when attempting to set a branch Given the mapping we use (namely, a git head is a bookmark), it is better to error out with a hint.

git: remove obsolete todo item The changes in 02c47b74366c cleaned up the requirement check.

tests: don't run test-update-atomic.t on chg I am unable to find a good way to make `showwrites` extension in it to work with chg. Also putting the use of showwrites inside `if no-chg` will defeat the purpose of test, so I just made the test no-op on chg.

tests: don't run couple of tests related to extensions loading with chg The couple of files test extensions loading and debugging that. It sets `devel.debug.extensions` to True to do that. Either we have to restart chg if this config is set or just don't run these tests on chg. I tried the first way by adding the config option to chgserver.py list of config subsections but that does not seem to work.

tests: conditionalize test-phases.t output for chg IIUC chg loads the ProgrammingError class which leads to it directly referencing it in error output. This makes the test pass on chg.