The prototype for vApplicationStackOverflowHook in section Stack Usage at http://www.freertos.org/Stacks-and-stack-overflow-checking.html has the wrong type for the task handle parameter:
void vApplicationStackOverflowHook( xTaskHandle *pxTask, signed portCHAR *pcTaskName );
It should not be a pointer to a task handle.
Hmm. The prototype is as per the extern in tasks.c - however the demos use both with and without the pointer, whereas the stack check macros themselves don't.
I will straighten this out. Thanks for the note.