Work-in-progress referential action trigger timing patch

Here's my current work in progress for 8.1 devel related to fixing the
timing issues with referential actions having their checks run on
intermediate states. I've only put in a simple test that failed against
8.0 in the regression patch and regression still passes for me. There's
still an outstanding question of whether looping gives the correct result
in the presence of explicit inserts and set constraints immediate in
before triggers.