Add tests for newtype-style tags

Author: marijnh

src/test/run-pass/newtype-polymorphic.rs

@@ -0,0 +1,16 @@
+tag myvec[X] = vec[X];
+
+fn myvec_deref[X](&myvec[X] mv) -> vec[X] {
+    ret *mv;
+}
+
+fn myvec_elt[X](&myvec[X] mv) -> X {
+    ret mv.(0);
+}
+
+fn main() {
+    auto mv = myvec([1, 2, 3]);
+    assert(myvec_deref(mv).(1) == 2);
+    assert(myvec_elt(mv) == 1);
+    assert(mv.(2) == 3);
+}

src/test/run-pass/newtype.rs

@@ -0,0 +1,10 @@
+tag mytype = rec(fn (&mytype i) -> int compute, int val);
+
+fn compute(&mytype i) -> int {
+    ret i.val + 20;
+}
+
+fn main() {
+    auto myval = mytype(rec(compute=compute, val=30));
+    assert(myval.compute(myval) == 50);
+}