Drop for-loop temporary at end of scope, fixes memory leak.

Author: graydon

src/comp/middle/trans.rs

@@ -2189,6 +2189,7 @@ fn trans_for(@block_ctxt cx,
         cx.build.Br(scope_cx.llbb);
         auto local_res = alloc_local(scope_cx, local);
         auto bcx = copy_ty(local_res.bcx, INIT, local_res.val, curr, t).bcx;
+        scope_cx.cleanups += clean(bind drop_slot(_, local_res.val, t));
         bcx = trans_block(bcx, body).bcx;
         bcx.build.Br(next_cx.llbb);
         ret res(next_cx, C_nil());