Fix validates_associated when documents are flagged_for_destroy
Merge pull request #3619 from cjbottaro/3618-validates_associated_flagged_for_destroy

Fix validates_associated when documents are flagged_for_destroy
Update changelog
Bring #3617 into master
Revert "Revert "Bit changed behaviour""

This reverts commit 670669cf40e1a28b6f0594a9c15643e1b2fc1083.
Tests passing on 2.6.0