[EXT] Removed the dependency on the "backup" gem

The `bundle install` command was failing on Ruby 1.8.7 because of:

    Gem::InstallError: httparty requires Ruby version >= 1.9.3.
    An error occurred while installing httparty (0.12.0), and Bundler cannot
    continue.

Mocked out the Backup gem's modules and class in the unit test.