Improve supervisor signal handler safety

Now should only be making async-signal-safe calls

src/Flare.h

@@ -26,15 +26,19 @@ public:
 
 	/**
 	 * Put the object in the "ready" state.
+	 * @param signal_safe  whether to skip error-reporting functionality that
+	 * is not async-signal-safe
 	 */
-	void Fire();
+	void Fire(bool signal_safe = false);
 
 	/**
 	 * Take the object out of the "ready" state.
+	 * @param signal_safe  whether to skip error-reporting functionality that
+	 * is not async-signal-safe
 	 * @return number of bytes read from the pipe, corresponds to the number
 	 * of times Fire() was called.
 	 */
-	int Extinguish();
+	int Extinguish(bool signal_safe = false);
 
 private:
 	Pipe pipe;