[RFC] Add intproprops.h

[Paul Eggert]

Ondřej Bílka wrote:
> If we go this way a intprops.h should be relicensed to LGPL2.1+

It's already licensed to LGPLv2+ so we're OK on this point.
(In Gnulib the license information for that file is in
modules/intprops.)

> does adding intprops.h to include
> directory look reasonable?

Looks OK to me (though as its author I'm biased....).