Brute force and ignorance workaround for tag-and-generic-obj; un-XFAIL it.

Author: graydon

src/comp/middle/trans.rs

@@ -4409,6 +4409,9 @@ fn trans_args(@block_ctxt cx,
                 }
             }
 
+            val = bcx.build.PointerCast(val, lldestty);
+        } else if (mode == ast.alias) {
+            auto lldestty = arg_tys.(i);
             val = bcx.build.PointerCast(val, lldestty);
         }
 

src/test/run-pass/tag-and-generic-obj.rs

@@ -1,5 +1,3 @@
-// xfail-stage0
-
 tag colour { red; green; }
 
 obj foo[T]() {