auto merge of #7488 : yichoi/rust/sanitize_utf8, r=huonw

back::link::sanitize support escape_utf8
fix #7486

Author: bors

src/librustc/back/link.rs

@@ -660,9 +660,10 @@ pub fn sanitize(s: &str) -> ~str {
             | '_' => result.push_char(c),
 
             _ => {
-                if c > 'z' && char::is_XID_continue(c) {
-                    result.push_char(c);
-                }
+                let mut tstr = ~"";
+                do char::escape_unicode(c) |c| { tstr.push_char(c); }
+                result.push_char('$');
+                result.push_str(tstr.slice_from(1));
             }
         }
     }