std: fix the non-stage0 str::raw::slice_bytes which broke in a merge

Author: erickt

src/libstd/str.rs

@@ -1051,7 +1051,7 @@ pub mod raw {
     /// If end is greater than the length of the string.
     #[cfg(not(stage0))]
     #[inline]
-    pub unsafe fn slice_bytes(s: &str, begin: uint, end: uint) -> &str {
+    pub unsafe fn slice_bytes<'a>(s: &'a str, begin: uint, end: uint) -> &'a str {
         do s.as_imm_buf |sbuf, n| {
              assert!((begin <= end));
              assert!((end <= n));