--pretty typed is broken for most programs

[marijnh]

The code path that resolves/typechecks the crate in driver::pretty_print_input is quite a bit out of sync with the equivalent code in driver::compile_input. It doesn't inject core, and it doesn't resolve external crates.

Probably the solution involves factoring most of compile_input into a function that operators on a crate and takes some arguments that allow callers to determine precisely which stages to run on it.