In this commit:
* Change the lit_int_unsuffixed AST node to not carry a type, since
it doesn't need one
* Don't print "(unsuffixed)" when pretty-printing unsuffixed integer
literals
* Just print "I" instead of "(integral)" for integral type variables
* Set up trans to use the information that will be gathered during
typeck to construct the appropriate constants for unsuffixed int
literals
* Add logic for handling int_ty_sets in typeck::infer
* Clean up unnecessary code in typeck::infer
* Add missing mk_ functions to middle::ty
* Add ty_var_integral to a few of the type utility functions it was
missing from in middle::ty
