lambdabot-core: add support for 'CODEPAGE' server command

  Our network uses CP1251, KOI8-R IRC ports and does
  not have ports with default UTF-8.

  But has 'CODEPAGE UTF-8' command.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
build fix for ghc-7.8: satisfy role constraints

Unfortunately, a nominal role is inferred for the type a in

  newtype ReaderT r m a = ReaderT (r -> m a)

causing a conflict between the declarations of LB in Monad.hs
and Monad.hs-boot. The fix is declare the nominal role
explicitly in the hs-boot file.
Merge branch 'master' of https://github.com/trofi/lambdabot
Merge branch 'master' of https://github.com/nomeata/lambdabot
implemented command-line option to disable insult messages
Fix Tell’s getMessages

to never return "Just []"