librustc: Make use statements crate-relative by default. r=brson

src/libsyntax/ext/log_syntax.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use base::*;
+use ext::base::*;
 use io::WriterUtil;
 
 fn expand_syntax_ext(cx: ext_ctxt, sp: codemap::span, tt: ~[ast::token_tree])