o Minor features:
    - The advertised platform of a router now includes only its
      operating system's name (e.g., "Linux", "Darwin", "Windows 7"),
      and not its service pack level (for Windows), or its CPU
      architecture (for Unix). This is part of ticket 2988.
    - Do not include the (git-XYZ) tag in published server descriptor
      platform lines. This is part of ticket 2988.
    - Allow packagers to insert an extra string in server descriptor
      platform lines by setting the preprocessor variable TOR_BUILD_TAG.
      This is part of ticket 2988.