Implement up to date check for tile directories

tools/src/main/java/com/threerings/media/tile/bundle/tools/BundleWriter.java

@@ -84,9 +84,19 @@ public class BundleWriter
     {
         if (_jar != null) {
             return _target.lastModified() > newest;
-        }
+        } else {
+            File []files = _target.listFiles();
+            if (files == null) {
                 return false;
             }
+            for (File file : files) {
+                if (file.lastModified() < newest) {
+                    return false;
+                }
+            }
+            return true;
+        }
+    }
 
     /**
      * Closes the writer.