Get comm_adapters building again

I accidentally removed this module from compilation awhile back, this adds it
back in.

Closes #11076

src/libstd/io/mod.rs

@@ -335,6 +335,9 @@ pub mod signal;
 /// Utility implementations of Reader and Writer
 pub mod util;
 
+/// Adapatation of Chan/Port types to a Writer/Reader type.
+pub mod comm_adapters;
+
 /// The default buffer size for various I/O operations
 static DEFAULT_BUF_SIZE: uint = 1024 * 64;