add needed fields for global libuv loop + bindings to manage from rust

adding two pointers fields to rust_kernel :(
.. have to do manual malloc/free for one of the fields, which feels wrong

src/rt/rust_kernel.cpp

@@ -24,6 +24,13 @@ rust_kernel::rust_kernel(rust_env *env) :
     non_weak_tasks(0),
     env(env)
 {
+    // set up storage of pointers needed to
+    // access the global loop.
+    global_loop_chan = 0;
+    global_async_handle = (void**)::malloc( // FIXME -- can use this->malloc()
+        sizeof(void*));                   // .. what do?
+    *global_async_handle = (void*)0;
+
     // Create the single threaded scheduler that will run on the platform's
     // main thread
     rust_manual_sched_launcher_factory launchfac;