Merge branch 'td/ref-filter-memoize-contains'

Merge branch 'td/ref-filter-memoize-contains'

'git branch --contains' and 'git for-each-ref --contains' have been
optimized to use the memoized commit traversal previously used only by
'git tag --contains', significantly speeding up connectivity checks
across many candidate refs with shared history.

* td/ref-filter-memoize-contains:
  commit-reach: die on contains walk errors
  ref-filter: memoize --contains with generations
  commit-reach: reject cycles in contains walk