We usually mutate some exceptions to OfflineImapError() and it is
a whole lot better if such exception will show up with the original
traceback, so all valid occurrences of such mutations were transformed
to the 3-tuple form of "raise". Had also added coding guidelines
document where this re-raise strategy is documented.
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>
