Job order should be kept as close to the original whitelist as possible

Thanks to the fix for bug990075 checkbox job reordering feature has been improved and the user can get specific feedback about what was changed to arrange the jobs in the whitelist in a topological order.

Unfortunately, the reordering algorithm doesn't take into account the original ordering in the whitelist and, consequently, the final job order is a valid one, but not one that is close to the original whitelist. If a job ordering that is as close to the original whitelist as possible is found, then the feedback to the user would be better since that would make clear what are the jobs that really need to be moved to satisfy the dependencies.