auto merge of #6019 : brson/rust/xfail, r=brson

Author: bors

src/libcore/num/strconv.rs

@@ -655,6 +655,7 @@ mod test {
     use option::*;
 
     #[test]
+    #[ignore(reason = "fails in x86")]
     fn from_str_ignore_underscores() {
         let s : Option<u8> = from_str_common("__1__", 2, false, false, false,
                                              ExpNone, false, true);