[Content Addressable] Install #1: Local RubyGems installation and activation

[OughtPuts]

• gem install ./<name>-<version>-<sha>.gem installs a local content-addressed file directly.
• require works after install, and a re-install is idempotent.
• The on-disk install directory is consistent between remote and local paths.
• Preserve the content address and real platform in serialized specifications and stubs so full_name can reconstruct
  <name>-<version>-<sha> without the original .gem file.

[OughtPuts]

@OughtPuts