When clicking run button while a sketch is running, it will be activated
again when the sketch is restarted. Previously it got deactivated by the
old sketch runner, because it was quitting after the new sketch runner
Pressing Run button twice launched two sketch windows, but only one of
them could be closed by Stop button. Pressing Stop had effect only after
sketch VM was launched.
Both of these issues are now fixed and buttons can handle a
frustration-relieving session of aggressive clicking, leaving one sketch
window if Run was the last button pressed or no window if Stop was the
last button pressed.