Long-running evaluations - visual feedback corrupts worksheet

[davidallsopp]

See also #77

The following code starts running, but the visual feedback (the 'spinner' characters) that are inserted into the worksheet after a few seconds, aren't cleaned up, which results in a compile error (value | is not a member of Unit possible cause: maybe a semicolon is missing before `value |'?)

object slow {
  println("start")                         
  Thread.sleep(5000)
}

However, following the slow-running task with further console output works fine:

object slow {
  println("start")                                //> start
  Thread.sleep(5000)
  println("end")                                  //> end
}