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This is safe because GHC never generates a fast call to a data constructor
worker: if the call is seen statically it will be eta-expanded and the
allocation of the data will be inlined. We still need to export the _closure
in case the constructor is used in an unapplied fashion.

I observed that the [CmmStatics] within CmmData uses the list in a very stylised way.
The first item in the list is almost invariably a CmmDataLabel. Many parts of the
compiler pattern match on this list and fail if this is not true.

This patch makes the invariant explicit by introducing a structured type CmmStatics
that holds the label and the list of remaining [CmmStatic].

There is one wrinkle: the x86 backend sometimes wants to output an alignment directive just
before the label. However, this can be easily fixed up by parameterising the native codegen
over the type of CmmStatics (though the GenCmmTop parameterisation) and using a pair
(Alignment, CmmStatics) there instead.

As a result, I think we will be able to remove CmmAlign and CmmDataLabel from the CmmStatic
data type, thus nuking a lot of code and failing pattern matches. This change will come as part
of my next patch.

This changes the new code generator to make use of the Hoopl package
for dataflow analysis.  Hoopl is a new boot package, and is maintained
in a separate upstream git repository (as usual, GHC has its own
lagging darcs mirror in http://darcs.haskell.org/packages/hoopl).

During this merge I squashed recent history into one patch.  I tried
to rebase, but the history had some internal conflicts of its own
which made rebase extremely confusing, so I gave up. The history I
squashed was:

  - Update new codegen to work with latest Hoopl
  - Add some notes on new code gen to cmm-notes
  - Enable Hoopl lag package.
  - Add SPJ note to cmm-notes
  - Improve GC calls on new code generator.

Work in this branch was done by:
   - Milan Straka <fox@ucw.cz>
   - John Dias <dias@cs.tufts.edu>
   - David Terei <davidterei@gmail.com>

Edward Z. Yang <ezyang@mit.edu> merged in further changes from GHC HEAD
and fixed a few bugs.

This is patch that adds support for interruptible FFI calls in the form
of a new foreign import keyword 'interruptible', which can be used
instead of 'safe' or 'unsafe'.  Interruptible FFI calls act like safe
FFI calls, except that the worker thread they run on may be interrupted.

Internally, it replaces BlockedOnCCall_NoUnblockEx with
BlockedOnCCall_Interruptible, and changes the behavior of the RTS
to not modify the TSO_ flags on the event of an FFI call from
a thread that was interruptible.  It also modifies the bytecode
format for foreign call, adding an extra Word16 to indicate
interruptibility.

The semantics of interruption vary from platform to platform, but the
intent is that any blocking system calls are aborted with an error code.
This is most useful for making function calls to system library
functions that support interrupting.  There is no support for pre-Vista
Windows.

There is a partner testsuite patch which adds several tests for this
functionality.

We still have
    insertList, insertListWith, deleteList
which aren't in Data.Map, and
    foldRightWithKey
which works around the fold(r)WithKey addition and deprecation.

This major patch implements the new OutsideIn constraint solving
algorithm in the typecheker, following our JFP paper "Modular type
inference with local assumptions".  

Done with major help from Dimitrios Vytiniotis and Brent Yorgey.

Wrote a generic function to extend dataflow results for safe foreign calls.
Should be able to throw it away when we change the representation of safe foreign calls.

The type of the CmmLabel ctor is now
  CmmLabel :: PackageId -> FastString -> CmmLabelInfo -> CLabel
  
 - When you construct a CmmLabel you have to explicitly say what
   package it is in. Many of these will just use rtsPackageId, but
   I've left it this way to remind people not to pretend labels are
   in the RTS package when they're not. 
   
 - When parsing a Cmm file, labels that are not defined in the 
   current file are assumed to be in the RTS package. 
   
   Labels imported like
      import label
   are assumed to be in a generic "foreign" package, which is different
   from the current one.
   
   Labels imported like
      import "package-name" label
   are marked as coming from the named package.
   
   This last one is needed for the integer-gmp library as we want to
   refer to labels that are not in the same compilation unit, but
   are in the same non-rts package.
   
   This should help remove the nasty #ifdef __PIC__ stuff from
   integer-gmp/cbits/gmp-wrappers.cmm
   

1. Stack overflow fixed by making dataflow monad strict in the state.
2. Out of memory fixed by "forgetting" lastoutfacts in the dataflow monad
   where we should. We were creating an unnecessarily long list that grew
   exponentially...

Among others:
- Fixed Stg->C-- translation of let-no-escapes -- it's important to use the
  right continuation...
- Fixed infinite recursion in X86 backend (shortcutJump mishandled infinite loops)
- Fixed yet another wrong calling convention -- primops take args only in vanilla regs,
  but they may return results on the stack!
- Removed StackInfo from LGraph and Block -- now in LastCall and CmmZ
- Updated avail-variable and liveness code

The interesting examples talk about our story with heap checks in
case alternatives and our story with the case scrutinee as a Boolean.

o The linear-scan register allocator sometimes allocated a block
  before allocating one of its predecessors, which could lead
  to inconsistent allocations. Now, we allocate a block only
  if a predecessor has set the "incoming" assignments for the block
  (or if it's the procedure's entry block).
o Also commented out some tracing code on the new codegen path.

Before: building a closure that would build an SRT given the top-level
SRT. It was somewhat difficult to understand the control flow, and it
may have had held onto some data structures long after they should be dead.
Now, I just bundle the info we need about CAFs along with the procedure
and directly call a new top-level function to build the SRTs later.