
Simplify the test that errors out if we're not selfupdating with the needed power: bail out right away if $installing_user doesn't own ${prefix}.
Also improve some of the comments we output.

git-svn-id: 620571fa9b4bd0cbce9a0cf901e91ef896adbf27@32537 d073be05-634f-4543-b044-5fe20cf6d1d6

danchr/macports-base,macports/macports-base,danchr/macports-base,macports/macports-base,neverpanic/macports-base,neverpanic/macports-base