Currently, the Date header in mbox views is incorrect;
datetime.datetime.utctimetuple assumes that the date is in the local
timezone, but we keep all dates as UTC.
This change replaces utctimetuple with a manual calculation of the
seconds-since-epoch timestamp, which email.utils.formatdate requires. We
add a testcase for this too.
Reported-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jeremy Kerr <jk@ozlabs.org>