* Use "math.h" instead of <math.h>.
* Use bit twiddling.  This requires inclusion of math_private.h
  and inclusion of float.h in s_roundl.c.  Raise invalid exception.
* Use literal integer constants where possible.  Let the compiler
  do the appropriate conversion.
* In s_roundf.c, use an F suffix on float constants instead of
  promoting float to double and then converting the result back
  to float. In s_roundl.c, use an L suffix.
* In s_roundl.c, use the ENTERI and RETURNI macros.  This requires
  the inclusion of fpmath.h and on __i386__ class hardware ieeefp.h.

Reviewed by:	bde