branchmap: Add a test about writing branchmap and aborted transaction It turn out that we update the branchmap on disk whenever we recompute it… including in a middle of a transaction. This means writing the new branchmap too early (the changeset are not visible yet) and worse… it mean writing branchmap for transaction we rollback. so we introduce a test to highlight the issue (and prevent it to regress in the future). Differential Revision: https://phab.mercurial-scm.org/D12126

dirstate-v2: rename the configuration to enable the format The rename of the old experimental name was overlooked before the 6.0 release. We rename everything to use the new name (and keep the released name as an alias for compatibility). Differential Revision: https://phab.mercurial-scm.org/D12129