Copyright notices

[Richard M. Stallman]

Our lawyer says it is ok if we add, to each file that has been in Emacs
since Emacs 21 came out in 2001, all the subsequent years.  We don't
need to check whether *that file* was changed in those years.
It's sufficient that *Emacs* was changed in those years (and it was!).

For those files that have been added since then, we should add
the year it was added to Emacs, and all subsequent years.

This is much easier than before, since it doesn't require checking anything
except whether the file was added after Emacs 21 and (if so) what
year it was added in.

Can people please start the work over, based on this advice?