tor/changes/fancy_testing

  o Build features:

    - Tor now builds each source file in two modes: a mode that avoids
      exposing identifiers needlessly, and another mode that exposes
      more identifiers for testing. This lets the compiler do better at
      optimizing the production code, while enabling us to take more
      radical measures to let the unit tests test things.

    - The production builds no longer include functions used only
      in the unit tests; all functions exposed from a module for
      unit-testing only are now static in production builds.