rustc: Make test/run-pass/generic-tag-alt.rs valid Rust; it was passing a dynamically-sized value by value instead of by alias

Author: pcwalton

src/test/run-pass/generic-tag-alt.rs

@@ -2,7 +2,7 @@ tag foo[T] {
   arm(T);
 }
 
-fn altfoo[T](foo[T] f) {
+fn altfoo[T](&foo[T] f) {
   auto hit = false;
   alt (f) {
     case (arm[T](?x)) {