libextra: Rename the actual metadata names of libcore to libstd and libstd to libextra

src/libsyntax/ext/pipes/ast_builder.rs

@@ -13,6 +13,9 @@
 // To start with, it will be use dummy spans, but it might someday do
 // something smarter.
 
+use core::prelude::*;
+
+use abi::AbiSet;
 use ast::ident;
 use ast;
 use codemap::span;