Add support for Rails 5.1+ AR Dirty changes

[jjuliano]

from saved_changes? to has_changes_to_save?, column_was to column_in_database and changed to changed_attribute_names_to_save. Check version string for each changes for backward compatibility.

[coveralls]

Coverage decreased (-0.3%) to 97.808% when pulling 81d02b2 on jjuliano:master into 7764bf5 on stefankroes:master.

[khustochka]

saved_changes? and has_changes_to_save? have different semantics. saved_changes? is true if there were any changes when an instance was saved last time. has_changes_to_save? (which is an alias to changed?) is true if there are unsaved changes.

With this change touch_ancestors_callback is never called, two more tests fail. Tested with AR 5.2.0.

[kbrock]

@khustochka thanks for the insight. It sounds like save_changes? is the one we till want to use

[kbrock]

thank you for diving into this. I'm trying to make some cleanup to make this easier to get fixed

[kbrock]

This is great stuff.

• I added appraisals for 5.2
• I changed the changed check to just use_was
• I got the tests passing (though I'm unsure if they are false positives)
• I used your fix for dangerous errors

Could you rebase and then help me understand the various methods that you all suggest instead of usingancestry_was?

Thanks for this PR. It is helping me get up to date with 5.2.

ASIDE: I'm looking at replacing child_ancestry with path_ids_was, ancestry withancestry_ids and ancestry_was with ancestry_ids_was everywhere. Keep that in mind as we are going through this code.

[kbrock]

I do have a branch that uses ids instead of the ancestry strings. but I've separated that.

I did need to revisit this. I've put together #387 instead. Hope that will meet our needs