Hardening of POP3 and SMTP communication:
SMTP: Decrement failure counter when no possible message send
occurred. This way, K-9 will only stop attempting to send messages
for which a possible successful send occurred, but K-9 could not
detect. Any message that is known to have completely failed to send
will be reattempted indefinitely.
POP3: Some reworking of Exception handling. Also, if it is not
possible to get a "message number" for the UID of the message that is
being deleted, conclude that the message has already been deleted on
the server. Mark this as a permanent error, so that it gets removed
from the pending actions queue.
MessagingController: Look for the permanentFailure flag on the
MessagingException, and if a pending action raised a permanent
failure, remove the pending action from the queue so that it will not
be re-attempted nor block later requests.
