Reorganise the way primops are done.  Most of the information about
primops, their types and relevant attributes is in prelude/primops.txt.
A supporting program in fptools/ghc/utils/genprimopcode reads this
file and generates various bits of code which are #include'd into
prelude/PrimOp.lhs.  Eventually this mechanism will be extended to
generate PrelGHC.hi and C code for primops in the bytecode evaluator.

Also, add a few primops for creating, reading and writing BCOs.