Store items and decls in vecs to preserve input order, index externally. Implement block-local name lookup.

Encode and decode tag types in dwarf properly. Add list module to std. Shift rustc to use std.util.option. Fix various dependent bugs. Closes #73.

Patchwork of attempted fixes to effect system and gc system; eventually give up and disable it entirely in the runtime. Will need extensive reworking.

Translate a bunch of the material (lltrans, llasm, abi) from rustboot to rustc, and move files around.