Per-test decorator syntax for test runner

[Jonathan Lange]

It would be really nice to be able to specify a test runner (e.g. RunTest) on a per-test basis using decorator syntax. That way tests with special running needs would not have to be split into separate classes. Ideally, this would not require the use of a special loader.

e.g.

{{{
  class TestFoo(TestCase):
    def test_normal(self):
      pass
    @use_runner(DeferredRunTest)
    def test_deferred(self):
      return defer.succeed(None)
}}}

Spelling can vary.

[Robert Collins (lifeless)]

This would be nice at many scopes:
 - test
 - class
 - module [perhaps spelt via load_tests at this scope]
 - testscenarios