bug#15108: Updated package dependencies

[Drew Adams]

> > ;; Package-Requires: ()
> 
> This will cause a dependency on `((nil (0)))' right now, I will fix
> that. May I ask why you wouldn't just leave the header out of the file
> or leave it empty? Just out of curiosity, this should work the same way
> as Emacs 24.3 I'm sure.

>From correspondence with people at MELPA, `Package-Requires' seems to be
required.  And being present with an empty list tells human readers that
the package has no dependencies.  (If absent, you don't get that explicit
info, and you might be wrong in assuming it.)

> > And most of the others (of mine) use this way (perhaps covered by
> > your 3rd, perhaps not, depending on your spec):
> >
> > ;; Package-Requires: ((fit-frame "0"))
> 
> This produces a dependency on `((fit-frame (0)))' with my patch
> installed, according to `package-buffer-info'.

It should mean that the library in which it is found requires library
`fit-frame', and any version of `fit-frame' is sufficient.  (Any real
version # is >= 0.)

Dunno what that syntax with 0 instead of "0" is.  Is is supported?
Does it mean something different from ((fit-frame "0"))?

> > See also bug #14941 (still unanswered, so far).
> 
> I will look at it, if you don't mind.

Thx.