Register snapshots and switch logging over to use of log_full or #error / #debug.

src/test/compile-fail/do-while-constraints.rs

@@ -4,7 +4,7 @@ fn main() {
     let y: int = 42;
     let x: int;
     do  {
-        log y;
+        log_full(core::debug, y);
         do  { do  { do  { x <- y; } while true } while true } while true
     } while true
 }