I want to add that, personally, I think the word "master" is much more interesting and descriptive than the word "main", if you think of it like a "master record". In this context, the master record was the authentic, trusted recording that the other copies were supposed to be based on or compared to.
Also, I think that the word "main" is just as bigoted and non-inclusive as "master". I mean, what can be more demeaning than saying that one branch is the "main" one and in some sense more important than the others? If we are going to have a "main" branch, than I think it should be democratically decided which one that is. Further more, there should be some regular rotation so that no branch gets to be the main branch all the time. -- Christopher Howard