bug#14591: New keyword :local for defcustom

[Stefan Monnier]

> This patch adds a new keyword :local to defcustom, to simplify cases like

> (defcustom some-var some-val
>    "A very long description
> filling many lines
> ...
> ...
> ..."
>   ;; some keywords)
> (make-variable-buffer-local 'some-var)

Problem is: most/all of those are in themselves problematic, because
Customize handles buffer-local variables very poorly.


        Stefan