Fixes T12464. Moves "arc upload" to SHA256 where applicable.
- Maniphest Tasks
- T12464: Move away from SHA1 in Files
- rARC3512c4ab86d6: (stable) Promote 2017 Week 14
rARCa59cfca5f190: Upgrade "arc upload" to use SHA256
Ran arc upload against a server with D17620 twice, saw it skip the actual upload the second time.