src: remove HandleWrap instances from list once closed

This allows keeping `BaseObjectPtr`s to `HandleWrap` instances.
Previously, the pointer kept the `HandleWrap` object alive, leaving
the Environment cleanup code that waits for the handle list to drain
in a busy loop, because only the `HandleWrap` destructor removed
the item from the list.

PR-URL: #165
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

src/handle_wrap.cc

@@ -131,6 +131,7 @@ void HandleWrap::OnClose(uv_handle_t* handle) {
   wrap->state_ = kClosed;
 
   wrap->OnClose();
+  wrap->handle_wrap_queue_.Remove();
 
   if (!wrap->persistent().IsEmpty() &&
       wrap->object()->Has(env->context(), env->handle_onclose_symbol())