Revert Command Ignores Dependencies

[theory]

The revert command does not validate dependencies. It should be updated to check that a change to be reverted is not required by some other change.

[theory]

I think this is going to be a fairly significant change. Currently, dependencies are just stored as strings from the as_string method from App::Sqitch::Plan::Depend -- more or less the dependency just as it was passed to Sqitch by the user. However, it will need to resolve those to IDs in order to validate them. I think the way to do that is going to be to store them. So on deploy, rather than store dependencies in arrays, I think we need to store them in another table, where a FK constraint has the ID that the dependency resolved to, and other columns have the as_string representation of the dependency and a boolean to indicate whether it is required or conflicting.

So that will have to be for the next release, I think. Need to get cross-project dependencies out now.

[theory]

Fixed and merged as of 1258b94.