F3 not only starts simulation, but ends it as well.

```
Accidentally pressed F3 while pressing F5 and was surprised when it closed 
simulation since I had seen F11 was used to exit simulation.  Looked and saw 
that F3 was used to run Simulation.  Dunno if you want to make it so F3 starts 
and ends simulation. If so then there would be no need of F11.
```

Original issue reported on code.google.com by `cazzro` on 19 Apr 2012 at 4:51
