Un-XFAIL mutable-alias-vec.rs. Was only failing due to a typo, but a …

…more thorough test revealed more bugs.

src/Makefile

@@ -345,7 +345,6 @@ TEST_XFAILS_X86 :=  $(MUT_BOX_XFAILS) \
                     test/run-pass/generic-fn-infer.rs \
                     test/run-pass/generic-fn-twice.rs \
                     test/run-pass/generic-recursive-tag.rs \
-                    test/run-pass/mutable-alias-vec.rs \
                     test/run-pass/mutable-vec-drop.rs \
                     test/run-pass/bind-obj-ctor.rs \
                     test/run-pass/task-comm.rs \

src/test/run-pass/mutable-alias-vec.rs

@@ -1,7 +1,17 @@
 // -*- rust -*-
 
-fn grow(mutable &vec[int] v) {
+use std;
+
+fn grow(&mutable vec[int] v) {
   v += vec(1);
 }
 
-fn main() {}
+fn main() {
+  let vec[int] v = vec();
+  grow(v);
+  grow(v);
+  grow(v);
+  auto len = std._vec.len[int](v);
+  log len;
+  check (len == uint(3));
+}