Add two trivial GNU Emacs compat functions

Michael Sperber writes:

 > Suggestions for better places to put these welcome ...  I'll wait until
 > the weekend before pushing this.

You are proposing this for core or for the fsf-compat package?

 > +;;;###autoload
 > +(defalias 'wholenump 'natnump)

Is this correct?  (Just checking that the semantics really are the
same.  In the grade school mathematics I was taught, they're
different, and the difference matters: it's zero.  So probably they
are, missing zero would be pretty annoying in applications I think.)

 > +;;;###autoload
 > +(defmacro declare-function (fn file &optional arglist fileonly))

I'd like this one to be in packages.  There are a number of APIs like
this one that would simplify VM, which I think is still usable with
21.4.  Preference isn't all that strong, it just struck me since I
used VM.