convert std::arc tests to use camel case ARCs

src/test/run-fail/issue-2444.rs

@@ -3,7 +3,7 @@
 use std;
 import std::arc;
 
-enum e<T: const send> { e(arc::arc<T>) }
+enum e<T: const send> { e(arc::ARC<T>) }
 
 fn foo() -> e<int> {fail;}
 

src/test/run-pass/bind-by-move.rs

@@ -1,7 +1,7 @@
 // xfail-test
 use std;
 import std::arc;
-fn dispose(+_x: arc::arc<bool>) unsafe { }
+fn dispose(+_x: arc::ARC<bool>) unsafe { }
 
 fn main() {
     let p = arc::arc(true);