Remove some uses of str_buf builtin. Issue #855

Author: brson

src/lib/str.rs

@@ -1,8 +1,6 @@
 export unsafe_from_bytes;
 
 native "rust" mod rustrt {
-    type sbuf;
-    fn str_buf(s: str) -> sbuf;
     fn str_from_vec(b: &[mutable? u8]) -> str;
     fn refcount<T>(s: str) -> uint;
 }

src/test/run-pass/item-attributes.rs

@@ -189,7 +189,7 @@ mod test_native_items {
         type sbuf;
 
         #[attr]
-        fn str_buf(s: str) -> sbuf;
+        fn unsupervise();
     }
 }
 

src/test/run-pass/native2.rs

@@ -1,8 +1,7 @@
 
 
 native "rust" mod rustrt {
-    type sbuf;
-    fn str_buf(s: str) -> sbuf;
+    fn unsupervise();
 }
 
 native "rust" mod bar = "" { }