#252 merging reverse mapping with forward mapping.

There is also an error in the `Mapper#reverse` method class.  The check on constant / expression has been fixed.

Also, the order of forward / reverse method is not relevant (as thought before). This is been assured by adding some tests.
No.. don't worry. I was not thinking of a container annotation. But, in essence you drag in all forward mappings right? 

Furthermore: I'm a bit worried by the parameter `configuredBy`. Perhaps `@ReverseMappings` (or `@ReverseMappingMethod`) is sufficient. You probably need to do some checking anyway if return-type matches parameter and vice versa. And what if it doesn't match? You need to give an error message for something that you already know.