[WARNING] change the package name for custom implementations

Hi,
till now if you provided implementation of derived attributes or
operations in your metamodel, you had to put it into
<model_package_prefix>.impl package. I would like to change it to
prevent problems with using standard packages like javax.* or org.omg.*.
The proposed solution is that MDR will look for implementations in
nbmdrimpls.<model_package_prefix> packages. For now I do not want to 
have this configurable using tags as it would slow the MDR down. We may 
introduce tags later if we find out that the impact on the performance 
is not too big, but anyway, the proposed solution would be the default 
one when no tags are used.
I would like to integrate this change tomorrow or during the weekend and
wanted to give you a chance to analyze the impact on your code and
comment, since this is a significant change.
Thanks,
Martin