worker: POSIX only supports workers from main thread (issue6460) The POSIX backend sets signal handlers for SIGINT (maybe avoidable) and SIGCHLD (necessary for waitpid). Python up to 3.9 only allow this from the main thread, so disable the worker feature otherwise. Differential Revision: https://phab.mercurial-scm.org/D9660

sharesafe: introduce config to disallow outdated shares if upgrade fails After this patch, we have config option to control all aspects of shares when share source is upgraded or downgraded. Differential Revision: https://phab.mercurial-scm.org/D9692

sharesafe: make warning about outdated share configurable If the source repository upgrades to use sharesafe mode, we show a warning in shares. This patch makes that warning configurable and some might not want their users see this warning. Differential Revision: https://phab.mercurial-scm.org/D9691