Add additional test for unboxing and bump version

aeneas/src/main/Version.v3

@@ -3,6 +3,6 @@
 
 // Updated by VCS scripts. DO NOT EDIT.
 component Version {
-	def version: string = "III-7.1756";
+	def version: string = "III-7.1757";
 	var buildData: string;
 }

test/variants/ub_rec07.v3

@@ -0,0 +1,38 @@
+//@execute 0=0; 1=12; 2=44; 3=288; 5=0
+
+type T<E> #unboxed {
+	case Leaf(x: E);
+	case One(a: T<E>.Leaf, b: T<E>.Leaf);
+	case Two(a: T<E>.One, b: T<E>.One);
+}
+
+def count1 = int.!<int>;
+def count2 = int.+;
+
+def main(a: int) -> int {
+	var x = make<int>(a, 3);
+	var y = make<(int, int)>(a, (4, 5));
+
+	return count(x, count1) + count(y, count2);
+}
+
+def count<E>(t: T<E>, num: E -> int) -> int {
+	match (t) {
+		Leaf(x) => return num(x);
+		One(a, b) => return 10 + count(a, num) + count(b, num);
+		Two(a, b) => return 100 + count(a, num) + count(b, num);
+	}
+}
+
+def make<E>(a: int, val: E) -> T<E> {
+	var d: T<E>;
+	var leaf = T<E>.Leaf(val);
+	var one = T<E>.One(leaf, leaf);
+	var two = T<E>.Two(one, one);
+
+	if (a == 1) return leaf;
+	if (a == 2) return one;
+	if (a == 3) return two;
+
+	return d;
+}