Add differently-typed refcount synonyms to _str and _vec.

src/lib/_str.rs

@@ -5,6 +5,7 @@ native "rust" mod rustrt {
   fn str_buf(str s) -> sbuf;
   fn str_len(str s) -> uint;
   fn str_alloc(uint n_bytes) -> str;
+  fn refcount[T](str s) -> uint;
 }
 
 fn is_utf8(vec[u8] v) -> bool {

src/lib/_vec.rs

@@ -6,6 +6,7 @@ native "rust" mod rustrt {
   fn vec_buf[T](vec[T] v) -> vbuf;
   fn vec_len[T](vec[T] v) -> uint;
   fn vec_alloc[T](uint n_elts) -> vec[T];
+  fn refcount[T](vec[T] v) -> uint;
 }
 
 fn alloc[T](uint n_elts) -> vec[T] {