#111 reduce hangs on exit

[arpi]

I am using reduce under kubuntu 18.04. With yesterdays release, when I try to exit reduce (by clicking the either close button of the window or the quit option in the file menu) it does not exit but becomes not responding, and has to be killed.
Surprisingly the quit; command works.

[Arthur Norman]

This shoul;d be fixed in a new snapshot and in the subversion code - the issue involved the GUI needing to communicate with the computation coire to instruct it to close down nicely.