Implement the RepeatTest Attribute.

Implemented RepeatTest attribute. When set to zero, the test is ignored as using IgnoreAttribute. 

For each test annotated with RepeatTest a test fixture is added to aggregate the tests, in this way it is possible to have the results grouped in a node with the total time of test runs.

Work with regular tests and using [TestCase] Attribute.

Here is an example of the xml output.
![dunitx-results](https://f.cloud.github.com/assets/842859/2218066/a206b730-9a27-11e3-93d7-9111e0db097f.jpg)