ww: separate package identity from declared name

lib/io/stream.ww

@@ -31,6 +31,8 @@
 
 package io;
 
+import errors;
+
 // Q2 layering (ratified): the file-arm of the handle dispatchers routes
 // to os.{read,write,close,lseek}; ww `os` plays Hare's `sys` role, so
 // `lib/io import os` is the correct direction (os is the import floor).