Fetch new files to a temporary location and then mv them to their final names if and only if the transfer succeeds.  This fixes the bug where distfiles would be left corrupted if the transfer was interrupted in the middle.
Fetch new files to a temporary location and then mv them to their final
names if and only if the transfer succeeds.  This fixes the bug where
distfiles would be left corrupted if the transfer was interrupted in
the middle.

git-svn-id: 620571fa9b4bd0cbce9a0cf901e91ef896adbf27@1046 d073be05-634f-4543-b044-5fe20cf6d1d6

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