Pretty sure this is a newbie question, but I really don't know so I'm going to ask.
I have an old feature branch (call it 
that hasn't been touched in about six months, because other projects took priority. Now it's being reactivated. The main branch M of my repository has undergone a LOT of changes and updates in those six months, but I don't think any of those changes conflict with the changes in B. However, "don't think" isn't good enough; I want to be sure.
So I want to copy all changes from M into B, except that if any changes in M conflict with changes I made in B, then I get notified and the B version doesn't get overwritten. Then I can reconcile the two versions and make sure B will still work as originally intended even with the changes from M. How do I do this?
