Undo/Redo on a constant does not update the Global constant list

[Kenneth Yrke Jørgensen]

To reproduce

1) Make a new net
2) Create a new constant
3) Undo the creation of this constant

The display now still shows the constant, however the model is updated correctly.

This also breaks for redoing a deleted constant.

Reported on ubuntu 10.10 64bit using version 2.0.2rc

[Jiri Srba (srba)]

Again, as before. I would sugget not to allow undo the creating of a constant (user can always delete it anyway).

[Kenneth Yrke Jørgensen (yrke)]

This will not solve the problem, as it will be possible to break consistent model behavior if not all elements does not support undo/redo, see bug #872815 for something similar of this an example of this, if activiation/deactiviation of components where a part of undo/redo history this would not be a problem.