rt: Remove the lock around upcall_vec_append. Add a test case. Closes #156.

src/rt/rust_upcall.cpp

@@ -470,7 +470,6 @@ upcall_vec_append(rust_task *task, type_desc *t, type_desc *elem_t,
                   rust_vec **dst_ptr, rust_vec *src, bool skip_null)
 {
     LOG_UPCALL_ENTRY(task);
-    scoped_lock with(task->kernel->scheduler_lock);
     rust_vec *dst = *dst_ptr;
     uintptr_t need_copy;
     size_t n_src_bytes = skip_null ? src->fill - 1 : src->fill;

src/test/run-pass/vec-ivec-deadlock.rs

@@ -0,0 +1,7 @@
+// xfail-stage0
+
+fn main() {
+    auto a = ~[ 1, 2, 3, 4, 5 ];
+    auto b = [ a, a ];
+    b += b;
+}