Re-jig SOURCE imports

* Do not have have an hs-boot file for Data.Typeable
* Instead make all the loops go through
     GHC.Err (just a couple of magic functions)
     GHC.Exception (some non-exceptional functions)

The main idea is
  a) don't involve classes in the hs-boot world
  b) loop through error cases where performance doesn't matter
  c) be careful not to SOURCE import things that are bottom,
     unless MkCore knows about them in eRROR_IDS, so that we
     see their strictness
Revert accidental change
Make GHC.Err depend on GHC.Integer

GHC relies internally on GCh.Integer.Type.mkInteger from integer-gmp,
but the dependency isn't visible to the build system, so we need to
add it here.
Comments
GHC.Err is no longer a boot module; no GHC/Err.lhs-boot