One more pre-release build available in the first post, before 2.13.0 will be posted on the website.
I've finished the first implementation of a three-way map merge, allowing to incorporate changes from another map into the active one - by specifying the base version both maps have been started from. This way all the changes that have been made to the loaded map will stay intact, and only the actual changes made to the other map will be applied to this one.
Just a quick textual description, before any tutorial is going to be posted eventually.
Let's say mapper A takes the map M1 and works on the harbour section of the mission, then saves it as M2.
Mapper B took the same map M1 and added a house in a different section of the mission, saving it as M3.
When merging M3 into M2, only the house from M3 will be imported into the active M2 map. Including layer changes and selection groups.
In case both mappers manipulated the same section of the map, the merger will still try to incorporate the changes, unless there's no reasonable way to do so - in this case the conflicting elements will be highlighted in the map and the mapper is asked to resolve it. By default, no conflicting change will be imported, unless the mapper chooses "Accept this change".
The whole thing is meant to form the algorithmic base for adding version control support to DR, most likely in the form of a Git plugin. This is something that has to be discussed though, feel free to share your thoughts.