An attempt to make tests deterministic.

The nondeterminism presently showing itself in
presentation/implicit-member is a consequence of the
presentation compiler tests relying on details of the
behavior of toString calls. We need to stomp this out,
but it will take a while. Based on the check file
changes enclosed with this commit, this will suffice
for the presentation compiler tests. A broader assault
will have to take place, but not yet.
Merge pull request #2566 from paulp/pr/nondeterminism

An attempt to make tests deterministic.