Final RC tagging suggestion

[Matt Frantz]

I would suggest that we adopt the convention of converting the final RC to
an official release by tagging the same commit that the final RC tag points
to.  That is, when we vote on something, we should be voting on an
RC-tagged commit.  If the vote passes, we would apply the tag to that
commit and not to wherever master happens to be.  Does that sound
reasonable?  Maybe this was the plan all along, but we were being a bit
more relaxed about the milestone release process, so I thought I'd confirm.