linkrev: use the right manifest content when adjusting linrev (issue4499) When the manifest revision is stored as a delta against a non-parent revision, '_adjustlinkrev' could miss some file update because it was using the delta only. We now use the 'fastread' method that uses the delta only when it makes sense. A test showcasing on the of possible issue have been added.

unpacker: fix missing arg for py2.4

branchcache: make _rbcrevslen handling more safe self._rbcrevslen is used to keep track of the number of good records on disk. It should thus not be updated before the records actually have been written to disk.