The docs say
appcfg.py --dump --app_id= \\
--url=http://.appspot.com/remote_api \\
--filename=
I found that I had to use download_data instead of --dump and --application instead of --app_id, for example:
appcfg.py download_data --application=app_id --url=http://etc --filename=file
Is it possible that you have two versions of app engine installed; one on your python path (a different version of appengine) and one in the /usr/local/share/google_appengine/VERSION directory (which reports 1.3.4)