Fixing bug with import privileged clashing with import hidden.
This caused a rather nasty name-leak, where catch from the prelude
was being given the type of catch from Exceptions.

Now, when you use import privileged Prelude (...) you also
need to do import Prelude, allowing you the option of
import Prelude hiding (...).

A bucket load of wibbles will follow in various libraries,
implementing this restriction.