bundle2: make the "hgtagsfnodes" part advisory This bundle2 part is about helping the client to warms its cache. There is no reason for it to be mandatory. So we mark it advisory.

branching: merge stable into default

branchcache: allow to detect "pure topological case" for branchmap We don't rum this detection every time we run the branchcache, that would be costly. However we now do it when running `hg debugupdatecache`. This will help existing repository to benefit from the fastpath when possible.