See if there is a way to execute both invokeDirectly and invokeAsSubprocess in variations of the same test

[andrewferrier]

Options being considered:

• nose-ittr: introduces an extra dependency.
• invokeBoth(): won't work, since tests assume it's only being executed once.

[andrewferrier]

Metaclasses look like an elegant approach: http://stackoverflow.com/a/20870875/27641