[ESS] distinguish busy from non-busy waiting

[Vitalie Spinu]

Sorry for late reply (I am travelling).
>>
>> Both of the following produce same result
>>
>> ## complete:
>> {
>>     Sys.sleep(10)
>> }
>>
>> ## incomplete:
>> {
>>     Sys.sleep(10
>>
>>

> I cannot reproduce this.  

You are probably having the default `ess-eval-visibly` set to t. I think most of
people switch to `nil` eventually because the default is very slow as it sends
the code line by line.

Indeed, when `ess-eval-visibly` is t, we probably can reliably track the prompt.

But then I don't understand your original problem. If you see trailing + that
means your code is incomplete, otherwise the program is busy.


  Vitalie