Enforce the checkout object to use an absolute path.

checkout.py

 # coding=utf8
 # Copyright (c) 2012 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.
 """Manages a project checkout.
 
 Includes support for svn, git-svn and git.
 """
 
 import ConfigParser
@@ skipping 84 matching lines @@
     self.project_name = project_name
     if self.project_name is None:
       self.project_path = self.root_dir
     else:
       self.project_path = os.path.join(self.root_dir, self.project_name)
     # Only used for logging purposes.
     self._last_seen_revision = None
     self.post_processors = post_processors
     assert self.root_dir
     assert self.project_path
+    assert os.path.isabs(self.project_path)
 
   def get_settings(self, key):
     return get_code_review_setting(self.project_path, key)
 
   def prepare(self, revision):
     """Checks out a clean copy of the tree and removes any local modification.
 
     This function shouldn't throw unless the remote repository is inaccessible,
     there is no free disk space or hard issues like that.
 
@@ skipping 607 matching lines @@
   def revisions(self, rev1, rev2):
     return self.checkout.revisions(rev1, rev2)
 
   @property
   def project_name(self):
     return self.checkout.project_name
 
   @property
   def project_path(self):
     return self.checkout.project_path