darcs patch: Replace FastInt with unpacked/newtyped Int

[Simon Peyton-Jones]

| This patch changes Unique from
|
|    data Unique = MkUnique FastInt
|
| to
|
|    newtype Unique = MkUnique Int
|
| Since this is performance critical code, I have checked the compiler output
| (core and stg), to check that it is really the same. The only difference is an
| improvement. mkUniqueGrimely no longer has to unbox and rebox its argument:

OK, good stuff.

| When also trying to change the FastInt in Var to an unpacked Unique I ran into a
| bug (#2070); The record selector realUnique will not be optimized at all.

I'm working on a patch for exactly this.  I plan to commit this week.

Simon