branchmap: move validity logic in the object itself In several place, We check if a branchcache is still valid regarding the current state of the repository. This changeset puts this logic in a method of the object that can be reused when necessary. A branch map is considered valid whenever it is up to date or a strict subset of the repository state. The change will help making branchcache aware of filtered revision. The change in keyword is expected. the branch cache is actually invalid after the amend. The previous check did not detected it.

branchmap: make update a method

branchmap: make update responsible to update the cache key The update function have all necessary data to keep the branchcache key up to date with its value. This saves assignment to the cache key that each caller of update had to do by hand. The strip case is a bit more complicated to handles from inside the function but I do not expect any impact.

branchmap: factorise changelog access in update This both improves readability and performance. Access to changelog of filtered repository currently have a minor overhead.