Problem with quoting in shell-command called from ediff-directories

[Lennart Borgman]

Here is another bug that depends on the problems with quoting. This time 
it is in `shell-command' that is called `ediff-append-custom-diff'. The 
file parameters need to be quoted but they are not.

If I understand our last discussion on quoting and different shells (on 
w32 escpecially) all that is needed is to use `shell-quote-argument' on 
those file parameters. Is that correct? Could you please add that, Michael?

Maybe there also should be a note in the doc string for `shell-command' 
about the need to use `shell-quote-argument' for file parameters?