INSTALL-xubuntu-12.10: Restored ability to paste multiple apt-get install commands.

We are reinventing the wheel. You will probably be as surprised as I was the first time I encountered trouble when pasting multiple 'sudo apt-get install -y \<packagename\>' commands.

Even though in INSTALL-xubuntu-12.10 I wrote:

    # The things below which are commands should be copied and pasted with thought,
    # one by one.

In practice I usually copy and paste many commands at once and find it very desirable to do so.

Last year someone else told me about the nifty -y option for apt-get install. It looked nice, so I tried it, but then pasting multiple commands failed. So I reverted back to the ugly 'yes | sudo apt-get install \<packagename\>' in INSTALL-xubuntu-12.10, so that I could successfully paste multiple lines at once.

The commit message for https://github.com/james-prior/astronomy-notebooks/commit/352380b020c48c4e87f218dd05dc822aded7d6c3 has a long explanation of this.

Please revert back to using 'yes | sudo apt-get install <packagename>' by pulling this request.