maint: Fix Face testing bug 1.9.2 revealed.

Ruby 1.8.7 is fairly lax about various bits of introspection, including that
we can't tell much about what arguments a block takes. Ruby 1.9.2 makes it
possible to do this, though.

Meanwhile, the Faces system uses this to make sure that scripts and actions
take the right set of arguments, to avoid surprises: failing early and
explicitly is better than failing at runtime.

Which, in final turn, exposes that I forgot to accept the right arguments in a
couple of my testing actions for Faces, but didn't notice because 1.8.7
doesn't check that, and I didn't test on 1.9.2.