#1443 WIP: the test still fails due to a chicken and egg problem: I need to isolate only Dofs related to a numbering subset to renumber them, but to know their NumberingSubset I need first their index... To break that I will change the weak dependancy: currently a Dof has a weak pointer to the NodeBearer, shortcircuiting the Node in the process... too bad the Node is the one to get the intel I need! I will therefore make the weak pointer toward the node, which itself will point toward the NodeBearer.