I was missing a 'quiet errors' option in rospack. I've added the '-q' option 
to quiet any 'top-level' error printing. This means that corruptions etc. are 
still reported, but the final result, like '[rospack] couldn't find package 
[foo]' isn't.

I needed this when using 'rospack find' from the roslib API.

Patch is against cturtle. 

Peter