auto merge of #14816 : theptrk/rust/unclear-comment, r=huonw

The old comment left it unclear if this is creating a random value or doing a check as to whether or not the generator is available or some other operation.

See: http://stackoverflow.com/questions/24153311/when-is-rng-gen-not-true

src/libstd/rand/mod.rs

@@ -60,7 +60,7 @@ use std::rand;
 use std::rand::Rng;
 
 let mut rng = rand::task_rng();
-if rng.gen() { // bool
+if rng.gen() { // random bool
     println!("int: {}, uint: {}", rng.gen::<int>(), rng.gen::<uint>())
 }
 ```