Clarify that we're using tests which expect the serial test protocol

Automake changed its defaults from using the serial protocol to using
the parallel protocol sometime between 1.11 and 1.13.

Our test suite makes a few assumptions which are valid for the serial
protocol, but not for the parallel protocol, which makes the test suite
fail with 1.13. As such, explicitly state that we want the serial
protocol so that things don't break with recent versions of automake.

A proper fix would be to make the test suite work with the parallel
protocol, but that's a lot more work than we have time for right now.

Conflicts:
	configure.ac
Remove missing, and re-enable integrityhuge test

This is a re-implementation of the same change on the master branch.
Updates