Merge Helper Script

[cookiengineer]

As retrokit currently diverged from upstream, it might be time to implement a merge helper script that selects the files with changes from upstream and pulls them in automatically. File creations after 2.34.1 need a manual review, as they could be potentially redundant (and already deleted) or not necessary at all.

This fork is currently based on 2.34.1, and when 2.36.0 is released this might be a necessity to not diverge too much from upstream when it comes to bugfixes and important security updates. As of today, WebKitGTK 2.34.3 is the latest stable version.