Added and functions dne() and sne() to test non-equality of floating-point variables

* Added and functions dne() and sne() to test non-equality of floating-point variables:
  * dne(x,y) = true if abs(x-y).gt.2*tiny(x)
  * sne(): same, but using single rather than double precision
  * in practice, dne() = .not.deq(); sne() = .not.seq()
Removed silly module construction in interpolate