vle-0.8.4

VLE 0.8.4

(See http://www.vle-project.org for details)

* devs: To allow a better debugging, we add a function allowing to store or dump a valid XML VPZ stream from the API of devs::Executive.
void devs::Executive::dump(std::ostream& out) const;

* extension difference equation: When a model connected to a generic DifferenceEquation model is removed, the number of connected models isn't updated correctly if some models have send your value.