src: add HandleScope in HandleWrap::OnClose

Fixes a 4 byte leak on handles closing. AKA The Walmart leak.

MakeCallback doesn't have a HandleScope. That means the callers scope
will retain ownership of created handles from MakeCallback and related.
There is by default a wrapping HandleScope before uv_run, if the caller
doesn't have a HandleScope on the stack the global will take ownership
which won't be reaped until the uv loop exits.

If a uv callback is fired, and there is no enclosing HandleScope in the
cb, you will appear to leak 4-bytes for every invocation. Take heed.

cc @hueniverse

src/handle_wrap.cc

@@ -134,6 +134,8 @@ HandleWrap::~HandleWrap() {
 
 
 void HandleWrap::OnClose(uv_handle_t* handle) {
+  HandleScope scope;
+
   HandleWrap* wrap = static_cast<HandleWrap*>(handle->data);
 
   // The wrap object should still be there.

src/node.h

@@ -238,6 +238,17 @@ node_module_struct* get_builtin_module(const char *name);
  */
 NODE_EXTERN void AtExit(void (*cb)(void* arg), void* arg = 0);
 
+/*
+ * MakeCallback doesn't have a HandleScope. That means the callers scope
+ * will retain ownership of created handles from MakeCallback and related.
+ * There is by default a wrapping HandleScope before uv_run, if the caller
+ * doesn't have a HandleScope on the stack the global will take ownership
+ * which won't be reaped until the uv loop exits.
+ *
+ * If a uv callback is fired, and there is no enclosing HandleScope in the
+ * cb, you will appear to leak 4-bytes for every invocation. Take heed.
+ */
+
 NODE_EXTERN void SetErrno(uv_err_t err);
 NODE_EXTERN v8::Handle<v8::Value>
 MakeCallback(const v8::Handle<v8::Object> object,