rmail -- rmail-summary movement

[Alfred M. Szmidt]

When moving in rmail-summary from message to message,
rmail-summary-previous-msg and rmail-summary-next-msg do not honour
the `deleted' label, and will happily move onto a deleted message.
The previous behaviour was that if a message was marked as deleted,
rmail-summary would skip over it.

If the message shows as `deleted' in rmail-summary, the behaviour
works, but the status of each message is cleared with a reissue of
rmail-summary.  (See previous mail entitled `rmail -- summary')