v10.0.1-bps-2: bps_patcher: Add checksum verification

This is exactly the same as upstream 10.0.1 (released on 2019-07-03), but with a critical fix for exheader replacement and support for BPS patches, along with some changes for easier troubleshooting.

I have no intention to add any other features or fixes.

If this becomes out of date, feel free to open an issue.