Backend hacking: NCG update

[Simon Marlow]

I now have zero unexpected failures in the test suite for the 'optasm'
way on x86 (not counting tests that are failing for reasons other than
bad code: the HEAD has a number of test failures at the moment, none of
which look fatal).

I'm now going to work a bit on improving the code quality, and maybe
take a look at the perf of the NCG to make sure we're not regressing
there.

A rough ToDo list for the backend-hacking branch (no particular order):

  - Profiling
  - Ticky-ticky
  - C backend
  - C-- parser
  - C-- generator
  - a few ToDos in compiler/NOTES and nativeGen/NOTES
  - ... anything else?

Good work guys!

Cheers,
	Simon