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We used to generated things like:
    extern StgWordArray (newCAF) __attribute__((aligned (8)));
    ((void (*)(void *))(W_)&newCAF)((void *)R1.w);
(which is to say, pretend that newCAF is some data, then cast it to a
function and call it).
This goes wrong on at least IA64, where:
    A function pointer on the ia64 does not point to the first byte of
    code. Intsead, it points to a structure that describes the function.
    The first quadword in the structure is the address of the first byte
    of code
so we end up dereferencing function pointers one time too many, and
segfaulting.

This merge does not turn on the new codegen (which only compiles
a select few programs at this point),
but it does introduce some changes to the old code generator.

The high bits:
1. The Rep Swamp patch is finally here.
   The highlight is that the representation of types at the
   machine level has changed.
   Consequently, this patch contains updates across several back ends.
2. The new Stg -> Cmm path is here, although it appears to have a
   fair number of bugs lurking.
3. Many improvements along the CmmCPSZ path, including:
   o stack layout
   o some code for infotables, half of which is right and half wrong
   o proc-point splitting