Cereal.Internal: use forever instead of sequence_ $ repeat

'repeat' generates an infinite list.  This can leak memory if GHC
fails to garbage collect the beginning of the list.
Update to conduit 1.0.0

conduit 1.0.0 dropped optional leftovers and upstream terminators from the
external API, so we make the following changes:

 * GSource -> Producer

 * GLSink -> Consumer

 * GLConduit -> Conduit

 * GInfConduit -> Conduit

Also, drop package bounds in the test-suite section, so we don't have to
maintain them in two places.  If the library built, then we should have
the right dependencies.
Version 0.7
Merge pull request #9 from joeyadams/follow-conduit-1.0.0

Update for conduit 1.0