Don't quit debugger when the program terminates, only after `quit`.

tests/debugger/nonempty_column_test.dart

 // Copyright (c) 2015, the Dartino project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE.md file.
 
 // Test that we get a meaningful breakpoint when breaking on a non-empty
 // column that does not point to the first sub-expression of the line.
 
-// DartinoDebuggerCommands=bf tests/debugger/nonempty_column_test.dart 13 22,r,bt,c
+// DartinoDebuggerCommands=bf tests/debugger/nonempty_column_test.dart 13 22,r,bt,c,q
 
 int foo() {
   int x = 2;
   int y = 3;
   int z = (y + 4) - (x + 5);
   return x + y + z;
 }
 
 main() {
   return foo() - 5;
 }