Use computed mask values in ForUtil

In the class ForkUtil, mask values have been computed and stored in static final vailables, but they are recomputed for every encoding, which may be unnecessary. 

anther small fix is that change

remainingBitsPerValue > remainingBitsPerLong

 to

remainingBitsPerValue >= remainingBitsPerLong

otherwise

if (remainingBitsPerValue == 0) {
 idx++;
 remainingBitsPerValue = bitsPerValue; 
}

these code will never be used.