IHaskell: allow cereal-0.4

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
src/IHaskell/IPython.hs: fix case sensitivity bug (Jinja has uppercase tarball name)

Fixes build failure on linux. Ideally IHaskell should mangle
the name itself though.

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>