Fix for issue #15: added support for BehaviorConfigs to WithFakes

In [issue 15](https://github.com/machine/machine.fakes/issues/15), you suggested `The()` should not be available from the `BehaviorConfig` because it isn't available from `WithFakes`. My change does not prevent you from using `The()` from the `BehaviorConfig`, but I'm not sure that's a problem. See the [example code here](https://github.com/shamp00/machine.fakes/blob/f8a1c93cd56fc5b9dbcc2ad0b488feead8b53f2c/Source/Machine.Fakes.Examples/9_Reuse/9_2_Reuse_via_BehaviorConfigs/MoodIdentifierSpecsWithFakes.cs).

This is my first GitHub pull request so I hope I did everything ok.