Merge cpan1: Implement the -T option with the notest method

Paul Johnson noted during the Swiss Perl Workshop that the -T switch in cpan(1) did not work, but that he didn't know why. I was able to answer "Because I didn't do it right!". I should have used the notest method, but I was trying to go through the configuration thinking CPAN.pm would pick it up automatically.

Now -T acts like -f, by calling its own method and making 'install' the first argument. If people want this all the time, they can set it in CPAN_OPTS (now documented!).

Also, I now set NONINTERACTIVE_TESTING and PERL_MM_USE_DEFAULT to true values unless values already exist. This is a change from previous behavior but I think it's the behavior that people expect. I thought about a -y switch (for "yes") to turn this on, too. Maybe I'll come back to that.