Fix some workflow problems wrt automation.

Fix some workflow problems wrt automation.

	- clearing automation points sets control to "off" rather than touch.
	- multiple touches on the same pass acts consistently (no more
	  fader jumps on mouse button press
	- use actual value for initial point rather than some arbitrary
	  default. clarify new semantics of add () (with_default->with_initial).
	- clean some whitespace
	- add guard points as needed in stop.
	- catch grab broken signal (i can't trigger it, but the docs seem
	  to think it is essential).