dirstate.walk: add a flag to let extensions avoid full walks...
dirstate.walk: add a flag to let extensions avoid full walks
Consider a hypothetical extension that implements walk in a more efficient
manner and skips some known-clean files. However, that can only be done under
some situations, such as when clean files are not being asked for and a
match.traversedir callback is not set. The full flag lets walk tell these two
cases apart.
