libintl updates

[William Orr <will%worrbase.com@localhost>]

Hey,

Here is some of my initial work on updating libintl. The first two patches are
small updates that remove some extraneous NULL checks. The third adds the
gettext functions that take a context argument to libintl, as detailed in
https://www.gnu.org/software/gettext/manual/gettext.html#Contexts

Let me know what I need to fix up.

Thanks,
William Orr