Rewrite each_path to allow performance improvements in the future.

Instead of determining paths from the path tag, we iterate through
modules' children recursively in the metadata. This will allow for
lazy external module resolution.

src/libextra/sync.rs

@@ -381,7 +381,7 @@ impl Sem<~[Waitqueue]> {
     // The only other places that condvars get built are rwlock.write_cond()
     // and rwlock_write_mode.
     pub fn access_cond<U>(&self, blk: &fn(c: &Condvar) -> U) -> U {
-        do self.access {
+        do self.access_waitqueue {
             blk(&Condvar { sem: self, order: Nothing })
         }
     }