Add a hybrid MIN_EXPR operator for integer and pointer.

Add a hybrid MIN_EXPR operator for integer and pointer.

This adds an operator to the unified table for MIN_EXPR which will
select either the pointer or integer version based on the type passed
to the method.   This is for use until we have a seperate PRANGE class.

	* range-op-mixed.h (operator_min): Remove final.
	* range-op-ptr.cc (pointer_table::pointer_table): Remove MIN_EXPR.
	(class hybrid_min_operator): New.
	(range_op_table::initialize_pointer_ops): Add hybrid_min_operator.
	* range-op.cc (unified_table::unified_table): Comment out MIN_EXPR.