* CORE-1348: Filter SQL visitors for rollback

Effectively, the applyToRollback="false" property of the modifySql change was being ignored.

The patch "works for me" and there surely are better ways to handle the problem of filtering the SqlVisitors selecting only the ones that apply to the rollback execution. Sadly I do not have enough knowledge of the structure of Liquibase to offer a better solution. Please see this pull request as a kind nudge to fix CORE-1348 ;-)