Fix benchmarks build.
Fixed `Alternative` instance

The `MonadPlus` super-class requires changing the `Alternative` instance
to use `mzero` and `mplus` instead of `empty` and `(<|>)`.
Merge pull request #83 from archblob/master

Fix benchmarks build.
Fix typo in Pipes/Core.hs
Merge pull request #84 from errge/patch-1

Fix typo in Pipes/Core.hs
Changed `print` to not terminate on broken pipe

Ending on broken pipe is usually not the desired behavior and it inconveniences
the user by forcing them to handle the `()` return value
Fixed `print`

I forgot to use `liftIO` and to qualify it to refer to the Prelude `print`