Add (failing) test case for #66.
Minor reformatting to aid legibility.
De-wild wildcards for singletonization.

I believe this fixes a latent bug, now tested in PatternMatching.
Revert "Add (failing) test case for #66."

This reverts commit 9e081847dd80d0f91a08bde73aedb7816ff4a2b5.

Conflicts:
	tests/compile-and-dump/Singletons/T66.hs