Automatically declare as «used» in an model instance, the packages

that are used to instantiate the model.

Indeed, the current parser forbids  the use of "uses" statements in a
model instanciation. I  could have changed the syntax,  but I was not
able to  find a satisfying  way to do  it. For instance, in  order to
declare that package Toto uses packege Util, should we write

	package Toto uses Util; = M(int, int, Util::foo);
?

The  semicolon is  really ugly.  And it  is so  easy to  realise that
package Util should be used...