[RFC] sparse SSA construction

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

Since it seems to be some interest on the subject and
to avoid duplicated work, here is a rewrite of sparse's
construction of the SSA form.

It's not using one of the classical algorithm but is
using something newer, simpler and often faster.
It's main advantage beyond the simplicity is that you don't
need to first build the whole CFG & linearized code to
to directly throw it away (or heavily transform it) as
it builds the SSA form directly during the linearization.

It's not finished code but it's working well (and is
effectively a bit faster and use less memory).
What's interesting for sparse now is that:
- the phi-noes are correctly placed
- uninitialized variables can be handled much more easily.

I don't feel it's needed to patchbomb the ML for the moment
so I'll only give the URL to the repo:

  git://github.com/lucvoo/sparse.git sssa