Due to a copy/paste error, the COPYING file and subsequently created files with the same content referred to the "Historical Permission Notice and Disclaimer - sell variant", not the proper MIT license.
For the code, use SPDX license identifiers instead, this way the copy-paste errors should be less likely to happen.
This is is effectively a license change, we'll need the ACK from all contributors. If you are listed here, please ACK in the comments and I'll add your Acked-by to the commit message, thanks.
List of committers with nontrivial patches:
No need for permission, things like typo fixes, etc.: