> The patch is not necessary. Under normal circumstances Tk does the right thing
> inside Tk_CreateErrorHandler() ... Tk_DeleteErrorHandler() blocks, there is
> no need to call XSync(), and in fact doing so is likely to hurt performance.

This is my argument, what "normal circumstances" are. Normal in my understanding
is to be sure (in the ensured sense) that there's a round trip with the X server,
i.e. stuff including X errors flow back to the client *before* Tk_DeleteErrorHandler().