Release plan; regression only

[Per Abrahamsen]

The GCC project has a policy that after a certain stage of the
development cycle, the only fixes being introduced are for
regressions.  The idea is that each release should (in principle) be
better than the previous, but it does not have to fix all problems of
the previous release.

There are obvious exceptions, such as bugs in totally new front-ends
can still be fixed, and doc fixes are always welcome.

I believe this helps them getting releases out of the door.

Maybe a similar policy for Emacs would be a good idea?