test: Fix name of bitv type

Author: brson

src/test/compile-fail/for-loop-decl.rs

@@ -6,7 +6,7 @@ import std::bitv;
 type fn_info = {vars: hashmap<uint, var_info>};
 type var_info = {a: uint, b: uint};
 
-fn bitv_to_str(enclosing: fn_info, v: bitv::t) -> str {
+fn bitv_to_str(enclosing: fn_info, v: bitv::bitv) -> str {
     let s = "";
 
     // error is that the value type in the hash map is var_info, not a box