In grml-x' completion there's the switch `fallback' missing. As well
as in the manpage.
And `help' is completing with brackets attached. Culprit's the leading
colon.

Furthermore, done in a separate diff, I guess we should stick to
double brackets for the test command here as well.
I first wanted to use check_com instead of `[[ -x ... ]]', but then
realised, that's not available in noninteractive shells. Besides,
it may be better to stay independent from grml's zsh-config for those
(non-grml) users, who just checkout the completion. Or am I missing
something in this regard?