Display a correct error message when taking a rock while another rock is being carried

I had a problem with defining a sound file for the new state. 
I defined in sound.ml that it should play a file called "take-no-space" and I created a new empty file under data/sounds by this name (with .wav extension).
Compilation went fine, but in run-time I got an error from res.ml
I only managed to work it out by doing () in sound.ml

The translations are Google based. I checked them 2-ways to make sure that they make sense. I hope they do, indeed...