Merge branch 'mh/clear-topo-walk-upon-reset'

Merge branch 'mh/clear-topo-walk-upon-reset'

The revision walking machinery uses resources like per-object flag
bits that need to be reset before a new iteration of walking
begins, but the resources related to topological walk were not
cleared correctly, which has been corrected.

* mh/clear-topo-walk-upon-reset:
  revision: free topo_walk_info before creating a new one in init_topo_walk
  revision: clear the topo-walk flags in reset_revision_walk