swift234

Tidy up IGF a bit, changing some ivars to be arguments to emitProlog, removing
dead methods, and moving emitInvoke to CallInvocation.

An interesting semantic change of this is that we're now calling getResultType
on the function type every time IGF is constructed, which exposed some latent
bugs.  Specifically two places in GenObjC are trying to extra curry level two 
from function types like "SomeObject -> (value : SomeObject) -> ()" which
doesn't make sense.  I switched them to get curry level 1, but this definitely
needs some close review.



Swift SVN r4852