Rewrite the bound change check and fix point check by using the bitwise
AND and bitwise OR operator. 
1. 'isChange' boolean value of Bounds class
'isChange' is true if the bounds have changed.
'isChange' is false if the bounds have NOT changed.
The bitwise OR is used to dijunct all the 'isChange' values while
propagating bounds for one single constraint.

2. 'isFixedPoint' boolean of ConstraintList 
'isFixedPoint' is true if the fixed point is reached.
'isFixedPoint' is false if the fixed point is not reached.
The bitwise AND is used to combine all the 'isFixedPoint' values while
propagating bounds for all the constraints in the list.