Backed out any attempt to turn off empty Seq comparisons. Got rid of the BackwardsCompatibility trait
and moved those two implicits as abstract members of EqualityPolicy, then make them implicit in the
old policies and non-implicit in the new policies. Also switched back the default policy mixed-into
Assertions from UncheckedEquality to TripleEquals. This required I revert some tests back, which also
made me realize I need to replicate those TripleEquals tests for UncheckedEquality at some point.