src: call uv_loop_delete() on exit in debug mode

Should make tracing with valgrind a little easier on the eye and
possibly help expose libuv handle lifecycle issues.

src/node.cc

@@ -3181,6 +3181,7 @@ int Start(int argc, char *argv[]) {
 #ifndef NDEBUG
   // Clean up. Not strictly necessary.
   V8::Dispose();
+  uv_loop_delete(uv_default_loop());
 #endif  // NDEBUG
 
   // Clean up the copy: