cmdutil: make getgraphlogrevs return revs in descending order

branchmap: takes filtered revision in account for cache calculation Tracking tipnode and tiprev is not enough to ensure validaty of the cache as they do not help distinguish a cache that ignored various revisions below tiprev. To detect such difference, we build a hash of all ignored revisions. This hash is then used when checking the validity of a cache for a repo.

branchmap: improve computation of target tip With revision filtering the effective revision number of "tip" may be lower than: len(changelog) - 1 We now use a more correct version preventing useless writing on disk in some case.