Added tests for derived predicate numbering.

These tests ensure that derived predicates are numbered correctly,
whether they are introduced by the domain, the problem, or both.

tests/data/normalization/normalization-6-2.pddl

@@ -0,0 +1,32 @@
+; tests derived predicates are correclty numbered
+; variation 2: derived predicates in domain only
+(define (domain test-normalization)
+	(:predicates
+		(test-predicate-0))
+
+	; introduces derived predicates 1 and 2
+	(:action test-action-1
+		:parameters
+			(?x)
+		:precondition
+			(or
+				(test-predicate-0)
+				(and
+					(test-predicate-0)
+					(test-predicate-0)))
+		:effect
+			(test-predicate-0))
+
+	; introduces derived predicates 3 and 4
+	(:action test-action-1
+		:parameters
+			(?x)
+		:precondition
+			(or
+				(test-predicate-0)
+				(and
+					(test-predicate-0)
+					(test-predicate-0)))
+		:effect
+			(test-predicate-0))
+)