Refactoring: Couple values and types into an object when passed around together

Handle closures in get_field_ty

Fixes #304

More validation tests

rustup

enable a test that waited for a rustc fix

Get the test suite working inside the rustc test suite

rustfmt

Except for error.rs, the result there looks rather ugly

Validation update

This is not complete yet, but it is enough to make unsized-tuple-impls work.

Turns out that tracking write locks by their lifetime is not precise enough,
but for now, we don't have an alternative.  Also, we need to force_allocate
what we acquire or else the memory will not be in the right state.

Don't rebuild miri even if nothing changed

Make cargo_miri a feature

1. Speeds up the common compilation path (no serde in the dependency tree)
2. Stage 1 rustc is enough (no serde -> no custom derive)

Prepare for splitting off static alloc ids from local alloc ids