Fix up r320731:
- Record mergeinfo for merges of r317518, r318647, r319197, r319198,
r319199, r319201, r320625, r320626, r320628, r320629, r320630, r320631,
r320632.
- Merge r319200, which (commit message notwithstanding) seems to have
gotten lost from the r320731 merge.