Here's a failing test for #1499
remove pytz, use aspen.utils.utc* instead
add a couple of helper methods to aspen.Response
fix how we patch `datetime.utcnow()` in tests
use `aspen.utils.to_rfc822` instead of the obsolete `rfc822.formatdate`
only send a session cookie when it's actually needed
temporarily copy to_rfc822() from aspen.utils

to be removed by #2384
raise a Warning if monkey-patched methods already exist
fix tests
Merge pull request #2385 from gittip/fix-session

Clean up how we handle sessions, cookies, and time zones