Execute `sudo dpkg --remove-architecture i386`, if Ubuntu is >= 12.10.

If the platform is Ubuntu 12.10 or more recent version,
execute `sudo dpkg --remove-architecture i386`,
in order to install only amd64 packages.

This commit refs #82.
Modify test for `multiarch` aptitude configuration.

This commit refs #82.
Merge pull request #82 from kazu634/id/82

[tahr] i386のパッケージをダウンロードしないようにする