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

...since we probably won't have this kind of typestate.

Remove old parser functions as well as support for old-style capture
clauses. Remove remaining old-style capture clauses.

I uncommented append_iter and made it compile. I hope it wasn't
horribly flawed in some other way... but if so, there was no comment
explaining how.

There was a FIXME noting that ty::enum_variants and typeck::check::
check_enum_variants both call eval_const_expr. I tried refactoring the
code so that check_enum_variants does all the work and enum_variants
just looks up cached results, but this turned out not to be easy because
several ty functions call enum_variants and it might get invoked on an
enum before that enum item has been typechecked. Instead, I just made
check_enum_variants update the enum_var_cache so that enum_variants
will never call eval_const_expr twice on the same const.