Add Paths as first-class types in configs.

scripts/slave/recipe_modules/generator_script/api.py

Index: scripts/slave/recipe_modules/generator_script/api.py
diff --git a/scripts/slave/recipe_modules/generator_script/api.py b/scripts/slave/recipe_modules/generator_script/api.py
index fd172dbcd2dc28d55230a62ecf394d03fc9912e7..edf9d557c22398399e4b741491acef4a7518414e 100644
--- a/scripts/slave/recipe_modules/generator_script/api.py
+++ b/scripts/slave/recipe_modules/generator_script/api.py
@@ -9,16 +9,16 @@ class GeneratorScriptApi(recipe_api.RecipeApi):
     """Run a script and generate the steps emitted by that script."""
     f = '--output-json'
     step_name = 'gen step(%s)' % self.m.path.basename(path_to_script)
-    if path_to_script.endswith('.py'):
+    if str(path_to_script).endswith('.py'):
       yield self.m.python(
         step_name,
         path_to_script, list(args) + [f, self.m.json.output()],
-        cwd=self.m.path.checkout())
+        cwd=self.m.path.checkout)
     else:
       yield self.m.step(
         step_name,
         [path_to_script,] + list(args) + [f, self.m.json.output()],
-        cwd=self.m.path.checkout())
+        cwd=self.m.path.checkout)
     new_steps = self.m.step_history.last_step().json.output
     assert isinstance(new_steps, list)
     yield new_steps