zsh-3.1.5-pws-9: clean up of Functions/Completion needed

["Andrej Borsenkow" <borsenkow.msk@sni.de>]

I suggest to split Functions/Completion/* in three (at least) different
groups.

1. must-have: run-time for new competion
These are helper functions, that actually make it work. It should be clearly
stated, that these functions are absolutely needed to even start with
completion. And that modification of these is as dangerous (or helpful :-)
as modification of zsh sources. Probably, FAQ should refer to them as
"read-only" for average users

2. should-have: completion for zsh builtins
Well, they actually belong to zsh and I'd like to have the same behaviour on
every zsh installation. Separating them from the case 1 is simply for
clarity and above reasons.

3. anything else
All other examples. They should be put into another (sub)directory, and
clearly marked as examples. As it stays now, simply sourcing
Functions/Completion/* gives me completion for PostScript, GIF etc I don't
care of, completion for GNU tar I don't have and completion for GNU cpio
that is completely wrong for my cpio. If anybody needs them - so be it, but
they should not be included by default.

cheers

/andrej