Support print0 with completions

[Ergus]

Hi:

Recently we are using global from emacs and it works pretty fine in most
of the case. We always use in the package consistently --print0 to
simplify the parsing code, BUT we found that --completion option does
not support --print0. It just ignores it and prints one
candidate/line. My request is simply to consistently add the same
behavior for print0 with completions.

Thanks in advance,
Ergus.

PD: BTW, I don't know if it is too complex, but if you have some shared
object where you expose some C bindings it may be very useful to provide
an emacs module, and inter-language support for global throw python for
example.