Merge branch 'en/backfill-fixes-and-edges' into seen

The 'git backfill' command now rejects revision-limiting options that
are incompatible with its operation, uses standard documentation for
revision ranges, and includes blobs from boundary commits by default
to improve performance of subsequent operations.

* en/backfill-fixes-and-edges:
  backfill: default to grabbing edge blobs too
  backfill: document acceptance of revision-range in more standard manner
  backfill: reject rev-list arguments that do not make sense