Issue #159 - add org.fest.util dependencies assertj-swing depends on

Hi Joel,

here is the addition of the dependencies to `org.fest.util` needed by `assertj-swing`.

There are a couple of things I would like to point your reviewing eyes to:

* My addition in `ErrorMessages` does not match the other messages but it therefore doesn't change the message of the thrown exception. Would you like to adapt the message of the exception to the ones other exceptions throw?
* __DRY__: Unfortunately I did sometimes repeat myself to a specific extend. Please tell me when that's to much repetition.
* The new methods (e.g. `newHashMap()`) in e.g. `Maps`, `Sets`, `Lists`.. should I implement to use them in the rest of `assertj-core`?
* Please review the changes to `Preconditions` as I'm not fully glad with them.