Add another test capturing violated expectation that SandboxViolation would be raised in a sandbox/hidden_setuptools context. Ref #440.

Refine test to not make additional references to exceptions in setuptools.sandbox, but instead create a bespoke unpickleable exception. Ref #440.

Remove check that would never succeed, because svn_utils always returns an integer and get_svn_revision always returns a non-empty string.