NAME
	FreeSignal -- free a signal bit

   SYNOPSIS
	FreeSignal(signalNum)
		   D0

	void FreeSignal(BYTE);

   FUNCTION
	This function frees a previously allocated signal bit for reuse.
	This call must be performed while running in the same task in which
	the signal was allocated.

   WARNING
	Signals may not be allocated or freed from exception handling code.

   NOTE
	Starting with V37, an attempt to free signal -1 is harmless.

   INPUTS
	signalNum - the signal number to free {0..31}.