Cross-repo recipe package system.

scripts/slave/unittests/recipe_simulation_test.py

 #!/usr/bin/env python
 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import os
+import shutil
 import sys
 
 import test_env  # pylint: disable=W0403,W0611
 
-from recipe_engine import simulation_test
-from slave import recipe_universe
+# Delete the old recipe_engine directory which might have stale pyc files
+# that will mess us up.
+shutil.rmtree(os.path.join(
+        os.path.dirname(os.path.dirname(os.path.dirname(os.path.dirname(
+            os.path.realpath(__file__))))),
+        'third_party', 'recipe_engine'),
+    ignore_errors=True)
 
-if __name__ == '__main__':
-  simulation_test.main(recipe_universe.get_universe())
+RECIPES_PY = os.path.join(
+    os.path.dirname(os.path.dirname(os.path.realpath(__file__))),
+    'recipes.py')
+
+args = [sys.argv[0], 'simulation_test'] + sys.argv[1:]
+os.execvp(RECIPES_PY, args)