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These include:
 - Stack size detection now includes function arguments.
 - Stack size detection now avoids stack checks just because of
   the GC block.
 - A CmmCall followed by a CmmBranch will no longer generate an extra
   continuation consisting just of the brach.
 - Multiple CmmCall/CmmBranch pairs that all go to the same place
   will try to use the same continuation.  If they can't (because
   the return value signature is different), adaptor block are built.
 - Function entry statements are now in a separate block.
   (Fixed bug with branches to the entry block having unintended effects.)
 - Other changes that I can't recall right now.

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.

The return values were getting put in a LocalReg
but that LocalReg needed to be stored into the enclosing
expression's return register (e.g. R1).

This patch is incomplete and will probably not compile by itself
but it is being recorded to help keep track of later changes.

This frees the Cmm data type from keeping a list of live global registers
in CmmCall which helps prepare for the CPS conversion phase.

CPS conversion does its own liveness analysis and takes input that should
not directly refer to parameter registers (e.g. R1, F5, D3, L2).  Since
these are the only things which could occur in the live global register
list, CPS conversion makes that field of the CmmCall constructor obsolite.

Once the CPS conversion pass is fully implemented, global register saving
will move from codeGen into the CPS pass.  Until then, this patch
is worth scrutinizing and testing to ensure it doesn't cause any performance
or correctness problems as the code passed to the backends by the CPS
converting will look very similar to the code that this patch makes codeGen
pass to the backend.