Fixed PropertyGetter and added corresponding unit test

Hi Alex,

First I would like to thank you for the framework: I'm working with MongoDB at the moment and nosql-unit helps me a lot in testing.

When I was writing a test, which involves Spring MVC, I faced the following problem: MongoDB @Rule cannot wire Mongo instance from Spring context if context variable class != ApplicationContext.class. In my case variable was declared as WebApplicationContext.

After some time of looking through source code I have got an assumption that PropertyGetter doesn't handle class hierarchy very well.

I prepared a small fix.
Could you please to consider it? Hope it will be useful for the project.


Thank you,
Anton