[LinuxCNC/linuxcnc Issue#112] the ja config update script Cancel button doesn’t cancel

In the current tip of master (8224ef91), launch a 2.7-style config. The linuxcnc launcher script pops up a dialog that among other things says “press Cancel to exit LinuxCNC”. But pressing Cancel starts linuxcnc with the original unmodified 2.7-style config.