title: Pressed CTRL-C to stop update, then updated GAE. Now: Transaction already in progress, but rollback not possible
body: <p>I was just updating my webapp on AppEngine but it got stuck while compiling. I pressed CTRL-C to abort, and appcfg.py gave me some output that it would rollback the update. Since this had happened multiple times today and I knew that there was an update, I downloaded the newest Python SDK, deleted the old one and tried to update again. Now it keeps telling me that there is still a transaction going on by myself, but whenever I try to rollback using <code>~/google_appengine/appcfg.py update rollback [my-app-directory]</code> it says that the Directory does not contain an rollback.yaml file. I am absolutely sure I did not delete any file in that directory. 
  Is there any way to solve this without having to use a new ID?</p>