This eliminates one of the panics introduced by 
the previous patch:
'First pass at implementing info tables for CPS'
  
The other panic introduced by that patch still remains.
It was due to the need to convert from a
  ContinuationInfo to a CmmInfo.
  (codeGen/CgInfoTbls.hs:emitClosureCodeAndInfoTable)
  (codeGen/CgInfoTbls.hs:emitReturnTarget)

This is a fairly complete implementation, however
two 'panic's have been placed in the critical path
where the implementation is still a bit lacking so
do not expect it to run quite yet.

One call to panic is because we still need to create
a GC block for procedures that don't have them yet.
(cmm/CmmCPS.hs:continuationToProc)

The other is due to the need to convert from a
ContinuationInfo to a CmmInfo.
(codeGen/CgInfoTbls.hs:emitClosureCodeAndInfoTable)
(codeGen/CgInfoTbls.hs:emitReturnTarget)

This version should compile but is still incomplete as it introduces
potential bugs at the places marked 'TODO FIXME NOW'.
It is being recorded to help keep track of changes.

This is a safety check-in, before I begin a cleanup.

At present it just annotates each block with a comment
indicating what local registers are live at the start
of the block.