[kutil] Update map iteration

Add an iterator type to kutil::map, and allow for each loops. Also
unify the compare() signature expected by sorting containers, and fixes
to adding and sorting in kutil::vector.

src/tests/container_helpers.h

@@ -6,8 +6,8 @@ struct unsortableT {
 
 struct sortableT {
 	int value;
-	int compare(const sortableT *other) const {
-		return value - other->value;
+	int compare(const sortableT &other) const {
+		return value - other.value;
 	}
 };