obshashrange: do not search for affected ranges above the highest we have It is a fast way to know we don't have an affected range for an affected revision.

obshashrange: do not search for affected stable range cache is unavailable Before this changeset we where resetting in all cases, and then looking for affected ranges. In addition is the stable range were not available, the functions silently returned no ranges affected. Now, do one or the other depending of the availability of the stable range cache. In practice we always do a broad reset because the code detecting affected changeset is currently buggy.