Reexport SubobjectResponsibility.

This exception seems to be generally useful, so it’s appropriate
to export it from StandardPrelude.
Fixes bugs in StandardPrelude type combinators.

These combinators need tests!
Removes Exception.raise from TypeVariant.

I don't understand why raising an Excpetion from a method
in the StandardPrelude should cause the C code generator
to generate bad code, but it does.  (The collectionsPrelude
raises many excpetions!) So, pro-tem, I indirectly raise
a NoSuchMethod exception instead.

The right solution for this is to re-define types so that the
method can actually be written.