[RFA/commit 2/2] Import gnulib's errno module.

[Joel Brobecker]

> Sorry, I meant to say that I wonder if the gnulib errno.h will cause
> problems, not that define.  I think that define is definitely obsolete
> at this point.

I can back the change out, if you think we need to think this over.
Conceptually, we need the module, because some of the other gnulib
modules depend on a full errno (mbrtowc, in particular), and I do
not think we can solve the problem without modifying gnulib.

-- 
Joel