bug#739: Suggested small functions to plug symmetry gaps

[Drew Adams]

> > How about `C-x r w' (for symmetry with `M-w') and move the 
> > binding of `window-configuration-to-register' to `C-x r W'?
> 
> I think that's a good idea.  I can't imagine that
> `window-configuration-to-register' is a command that's used a lot.

1. That's not a great assumption.

2. `C-x r M-w' is better for symmetry with `M-w'.

Plain `w' has symmetry with lots of other things in Emacs (write commands,
window commands,...).  `M-w' is ingrained in finger-memory as a copy operation.
Better to keep `w' for something that actually has a `w' in its name/meaning.

(Yes, I know that Dired uses `w' as `dired-copy-filename-as-kill', but that's
presumably because `M-w' is still available there and the aim was to avoid using
a prefix.)

3. With `M-w', if someone binds `ctl-x-r-map' to a (prefix) key (e.g., a shorter
one than `C-x r'), then s?he gets `M-w' on it, with its "copy" association.  As
opposed to getting just `w', with no such useful association.  E.g., `<f10>
M-w'.

4. I really don't care.  If the above helps, fine.