ENHANCED: CLP(ℤ): Reduce redundant propagator invocations during all_distinct/1 filtering

ENHANCED: CLP(ℤ): Reduce redundant propagator invocations during all_distinct/1 filtering

First, the current propagator is now logged and not re-triggered
during filtering. Second, and more significantly, all neq_num/2
constraints are scheduled and processed before more global constraints
are invoked. In this way, all the distilled information can be taken
into account by subsequently invoked global constraints.

These changes yield a 3-fold improvement in several Sudoku instances,
and a significant runtime reduction in social golfer instance 8-4-9.