#697 quitting "pd -jack" can hang Pd

[IOhannes m zmölnig]

if Pd starts the jackd automatically (which is the case if no jackd is running and you start "pd -jack"), and you then connect another application to jack (it is sufficient to start e.g. qjackctrl), quitting Pd becomes weird:
- the "pd" process terminates
- pd-gui still hangs around
- pd-watchdog starts signalling (as the non-existant pd process doesn't reply anymore)

system:
debian(wheezy/sid) i386
jackdmp 1.9.6
pd 0.43.0