[Portland] xdg-utils: common return values [CORRECT PATCH]

[Jeremy White]

> Hmm. How about build time including the xdg-include file in the scripts, but 
> still have it separated from xdg-utils-common-in?
> 
> This way we have
> - each script working stand alone
> - a file to include for scripts using xdg-utils (xdg-include or 
> xdg-utils-include), quite like a public header file
> - a file to separate common scripts parts into for easier development 
> (xdg-utils-common.in) quite like a private header file

To be honest, I think my first patch accomplished essentially
the same thing, but was simpler.

Thus, instead of having xdg-utils-common.in and
xdg-includes, just have a single xdg-utils-common
which provides both functions.

The downside is that we may end up with a lot of
cruft in xdg-utils-common that we might prefer be
internal use only, and now it's exposed to outside view.

I don't really feel all that strongly about it;
either way we solve it works for me.

I do think it would be really great, though, to provide
a named set of return codes and start being consistent
about using them by name, just for the the documentation
value I think it will bring.

Cheers,

Jeremy