Back out constructor/prefetch rewrite introduced mainly by 43245ada4a

Back out constructor/prefetch rewrite introduced mainly by 43245ada4a

It was shipped against the authors advice, while containing multiple known
bugs. After the expected bugreports went warnocked for over two weeks by the
new DBIC release team, it seems that the only way to partially restore the
release quality DBIC users have come to expect, is to currently throw this
code away until better times.

Should resolve RT#78456 and the issues reported in these threads:
http://lists.scsys.co.uk/pipermail/dbix-class/2012-July/010681.html
http://lists.scsys.co.uk/pipermail/dbix-class/2012-July/010682.html