Major and minor releases are no longer explicit branches.  Today we have the minor branch of `master` and the patch branch of `3.1.x`.  In the new model we'll have these as `master` and `stable` respectively.

We don't actually have a branch for major versions at all, today or with the new strategy.  We only have branches for bug fixes (patch level) and new, backwards compatible functionality (minor versions).

Major versions are backwards incompatible, and we're doing as much as we can to prevent incompatible changes from getting merged in anywhere.