rustc: Add a testcase for vector push (mutable aliases with *, really)

src/test/run-pass/vec-push.rs

@@ -0,0 +1,11 @@
+// xfail-stage0
+
+fn push[T](&mutable vec[mutable? T] v, &T t) {
+    v += vec(t);
+}
+
+fn main() {
+    auto v = @vec(1, 2, 3);
+    push(*v, 1);
+}
+