1.  Add primOpStrictness to PrimOp.lhs, and use it in
	- the strictness analyser
	- the simplifier
    to deal correctly with PrimOps that are non-strict.

   ToDo: use this new facility to clean up SeqOp, ParOp.

2. Fix the instance-decl-import bug, but printing de-synonym'd types
   in interface files.

3. Make the simplifier treat applications with an unlifted-type arg
   in the same way it would if the function was strict
   (in rebuild_strict)