Cosmetics
Refactor COPFinder to move the main logic to a data structure class

This makes the next step much less of a ridiculous exercise on c&p
coding. (And also avoids the evil of multiple inheritance by using
composition instead.)
Refactor OpTreeVisitorPerlCb for easier subclassing
COP-hint filtering visitor that calls Perl callbacks
Expose hinted CopFinder to perl
Round of fixing: proper initialization