3.0 features.html; 3.0.4 also has threadsafe libstdc++

[Jeff Donner]

Hi,

  I don't remember all the specifics but I believe that stringstream & perhaps string itself were 
made properly threadsafe in the 3.0.4 libstdc++; if I'm not mistaken about that, I think that's worth 
mentioning on the features page. 

Jeff