enable IEEE gentle failures in ELFUN and GROUP:

      USE, intrinsic :: ieee_exceptions
      LOGICAL :: ieee_crash
      CALL ieee_get_flag( ieee_overflow, ieee_crash )
      IF ( ieee_crash ) IFSTAT = 3
      CALL ieee_get_flag( ieee_divide_by_zero, ieee_crash )
      IF ( ieee_crash ) IFSTAT = 3
      CALL ieee_get_flag( ieee_invalid, ieee_crash )
      IF ( ieee_crash ) IFSTAT = 3

may need additional appropiate ieee flags at compilation;
only available with gfortran 5, ifort 16, nagfor 6.1 (etc).

Nick Gould
30/March/2017
