core: Inherit necessary unicode functionality

The unicode module remains private, but the normalization iterators require an
allocation, so some functionality needs to remain in libstd

Author: alexcrichton

src/libcore/lib.rs

@@ -61,6 +61,7 @@ pub mod container;
 
 /* Core types and methods on primitives */
 
+mod unicode;
 mod unit;
 pub mod any;
 pub mod bool;