Add len to str extensions

src/libcore/str.rs

@@ -1783,6 +1783,9 @@ fn is_not_empty() -> bool { is_not_empty(self) }
     "]
     #[inline]
     fn is_whitespace() -> bool { is_whitespace(self) }
+    #[inline]
+    #[doc ="Returns the size in bytes not counting the null terminator"]
+    fn len() -> uint { len(self) }
     #[doc = "
     Returns a slice of the given string from the byte range [`begin`..`end`)