This is a bug fix for a flawed patch I put in lk 2.4.19
(sg version 3.1.24) and has been carried through into
the 2.5 series. Thanks to Andy Polyakov
<appro@fy.chalmers.se> for pointing this out (more than once).

The sg.h header didn't get updated last time I submitted
an sg patch so this patch also addresses that.