This adds auto-assertion to `rustc_clean/dirty` and also implements
more comprehensive testing for
- src/test/incremental/hashes/enum_constructors.rs
- src/test/incremental/hashes/enum_defs.rs
- src/test/incremental/hashes/extern_mods.rs
- src/test/incremental/hashes/inherent_impls.rs
- src/test/incremental/hashes/statics.rs
- src/test/incremental/hashes/struct_constructors.rs
- src/test/incremental/hashes/type_defs.rs
trait_defs.rs and trait_impl.rs are blocked on a hard to triage
compiler ICE (at least hard for a newbie like me) having to do
with some DepNodes not getting computed for traits.
A FIXME has been added in the source to reflect this continued
work.
