rbKarel - can crash with pressing Run too quickly

```
What steps will reproduce the problem?
1. Start running, easiest to reproduce with single-step turned on
2. Press command-R
3. Press command-R very quickly again

What is the expected output? What do you see instead?
Cmd-R first time should trigger a Stop and second should go again. However, if
they are close
enough together, it crashes.

Workaround - discourage pressing command-r and click on the buttons instead,
which has enough
inbuilt delay to avoid triggering the problem.

```

Original issue reported on code.google.com by `dentaroo@gmail.com` on 26 May 2009 at 9:38