Enhancements: expect/result syntax sugar and better Mock.__repr__

[Daniel]

I have written two new methods for the Mock class that make it easier to perform expect(x).result(y). In addition, it adds a convenient way to 'inject' results into a sub-expression while constructing a larger test expression. Example syntax (sugar):

These are equivalent:

sweet: mock.func(arg) << value
sour: expect(mock.func(arg)).result(value)

And these are equivalent:

sweet: (mock.func(arg) >> value).value_func()
sour: expect(mock.func(arg)).result(value); value.value_func()

Implementation attached.

I have also included a __repr__ function for the Mock class that makes it easier to debug test failures. I know it should technically be submitted as a separate bug, but I'm lazy.

[Gustavo Niemeyer (niemeyer)]

By design, Mock objects do not have any special syntax attached to themselves, because that would conflict with the implementation of the same methods on real objects.