Further fixes to protection expiry:

Further fixes to protection expiry:
* Use RFC 2822-style date/time format instead of localized formatting for
  the expiry time in the protection form; while ugly, it actually works;
  a localized time is usually lossy (changing the time on submit) and
  more significantly will fail for any UI language that's not english!
* Rearrange some of the form display logic to handle error conditions
  a little more gracefully; invalid expiry format caused the form to
  be displayed twice.
* Should be nicer on session token expiration as well, showing the
  form instead of just an exception message.