Introduce an easier to follow "next" branch.

Introduce an easier to follow "next" branch.

The "pu" branch is a bit too hard to follow.  Let's introduce
"next" branch, which is slightly ahead of "master".  The topic
branches merged into it are not to be rebased, and changes to
the topic branches are first applied to them and then merged
into the "next" branch.  What this means is that the branch is
far easier to follow compared to the "pu" branch since there
will be no rewinding/rebasing involved.