This should be a snapshot transition.

 * Cleans up the algorithm
 * Move first pass to walk (second still folds)
 * Support part of a type/value namespace split
   (crate metadata and module indices still need to be taught about this)
 * Remove a few blatant inefficiencies (import tables being recreated for
   every lookup, most importantly)

(Have fun mergining your stuff with this.)

Remove redundant imports in lib (rustc doesn't like 'std' as a synonym for root within std.rc anyway)

rustboot: Don't use walk to traverse statements in type.ml; fixes redundant checking, improves diagnostics. Also report untyped slots.

Revert "rustboot: Emit an error instead of asserting in trans when a T is passed by value" due to test failures

This reverts commit ee901858.

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.

Move ports out into their own file, add data_message and make communication system use it (and proxies) instead of existing token scheme.

Added a message passing system based on lock free queues for inter-thread communication. Channels now buffer on the sending side, and no longer require blocking when sending. Lots of other refactoring and bug fixes.