[Yhc] Some more changes to core

[Isaac Dupree]

>>  Even better if the number was
>> essentially a line number or similar (clause number?), to make it even
>> more readable.
> 
> It can't be a line number, since you can potentially put two clauses
> on the same line. You could certainly do better with the desugaring,
> but I think a more annoying desugar problem comes with _LAMBDA's which
> crop up quite a bit, and have absolutely nothing tying them back to
> their original location.

How much in Core has an "obvious" translation from Haskell, such that 
different implementations or versions, can compile the same Haskell code 
and get the exact same Core text out?  If only local things like the 
details of how let/lambda-bound variables are named, vary, there is more 
possible separate compilation of separate files (or something like that...).

I think (line,column) is sufficiently unique identification? Maybe 200_4 
would represent line 200, column 4. (or "200.4"? By itself, that looks 
like a fractional number, which is bad)

Isaac