Start Pure Data in a subprocess.
		
		>>> from time import time, sleep
		>>> from os import path, getcwd
		>>> 
		>>> start = time()
		>>> # launching pd
		>>> pd = Pd(nogui=False)
		>>> pd.Send(["test message", 1, 2, 3])
		>>> 
		>>> def Pd_hello(self, message):
		... 	print "Pd called Pd_hello(%s)" % message
		...
		>>> pd.Pd_hello = Pd_hello
		>>> 
		>>> sentexit = False
		>>> # running a bunch of stuff for up to 20 seconds
		>>> while time() - start < 20 and pd.Alive():
		... 	if time() - start > 0.5 and not sentexit:
		... 		pd.Send(["exit"])
		... 		sentexit = True
		... 	pd.Update()
		...
		...
		Pd called Pd_hello(['this', 'is', 'my', 'message', 'to', 'python'])
		untrapped message: ['this', 'is', 'another', 'message']
		untrapped stderr output: "connecting to port 30322"
		untrapped stderr output: "python-connected: 0"
		untrapped stderr output: "python-connected: 1"
		untrapped stderr output: "from-python: test message 1 2 3"
		untrapped stderr output: "closing audio..."
		untrapped stderr output: "pd_gui: pd process exited"
		untrapped stderr output: "closing MIDI..."...
		Pd died!
		>>> pd.Exit()