Fix simplejson import for Mac OSX 10.5 users

BUG=none
TEST=Poor mac users should be able to use git-cl back again.

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@79932 0039d316-1c4b-4281-b951-d872f2087c98

git_cl.py

@@ -26,7 +26,8 @@ except ImportError:
     import json
   except ImportError:
     # Fall back to the packaged version.
-    from third_party import simplejson as json
+    sys.path.append(os.path.join(os.path.dirname(__file__), 'third_party'))
+    import simplejson as json
 
 
 from third_party import upload