Fix queries with date and date-time placeholder conditions

[andsip]

Fix queries with date and date-time placeholder conditions such as:

where("written_on < ?", Date.today)
where("written_on < ?", DateTime.current) 

This should fix #1243.

[aidanharan]

Could you add a few tests and update the CHANGELOG?

[andsip]

I don't see any tests that have been added in the last several changes in this code part.. Could you point me to the test file, where similar functionality is being tested already?