Squelch warning about intersperse() entering stdlib.

Presumably we'll want to switch to it when it standardizes, so we want
the build to break when it's time to move over.

src/bin/printmap.rs

@@ -40,6 +40,7 @@ fn main() {
   print_rows(world.map().rows());
 }
 
+#[allow(unstable_name_collisions)]
 fn print_rows<'a, T: ?Sized, U: ?Sized>(rows: Box<T>)
   where T: Iterator<Item = Box<U>> + 'a,
         U: Iterator<Item = &'a tile::Tile> + 'a