Add a test that exercises these cases in bind.

src/test/run-pass/fixed-point-bind-box.rs

@@ -0,0 +1,20 @@
+// xfail-stage0
+
+fn fix_help[A,B](@fn (@fn (&A) -> B, &A) -> B f, &A x) -> B {
+    ret f(@bind fix_help(f, _), x);
+}
+
+fn fix[A,B](@fn (@fn (&A) -> B, &A) -> B f) -> (@fn(&A) -> B) {
+    ret @bind fix_help(f, _);
+}
+
+fn fact_(@fn (&int) -> int f, &int n) -> int {
+    // fun fact 0 = 1
+    ret if (n == 0) { 1 } else { n*f(n-1) };
+}
+
+fn main() {
+    auto fact = fix(@fact_);
+    assert(fact(5) == 120);
+    assert(fact(2) == 2);
+}