[ghemical-devel] Constraint View Patch

[Donald Ephraim Curtis]

> You should also call model::SystemWasModified() if constraints are added, 
> removed or modified. I think this will solve the problem you found. When 
> you set the constraint "disabled", the change was saved into the model 
> object but it was not passed to the engine object, nor the engine object 
> was invalidated ; therefore the change did not affect anything in the 
> calculations and the bond length did not go back to normal.

I checkedthis out, it's getting called when you update the values of a
constraint but the constraint isn't getting changed in the engine.  I
don' know what the deal is.  To reproduce: constrain a bond to 1nm, then
remove he constraint, it doesn't go back to normal.