Overhaul pt-upgrade

pt-upgrade needs a serious overhaul to make it more helpful than cumbersome. At present, it has no limit on the number of sample queries it will spew. A consultant sent me its output from a run: there were 70k+ lines, but it was really only a few that were important. Plus, the tool doesn't handle errors gracefully, despite my initial efforts to make it do that.

This is the kind of tool that's all about the report. Chances are a lot will go wrong because it's often given less than optimal input, but it needs to make it clear which queries don't seem to upgrade well, which failed due to errors, etc.

With three versions of MySQL now (5.0, 5.1, and 5.5), I think this tool can be really helpful if it's not a pain to use.