IPrimitive comparisions & re-use

[VistianOpenSource]

Currently IPrimitives are directly compared and if their underlying type is different then they are immediately considered as not being suitable. No consideration is given to how the IPrimitive was created e.g. if they both came from Username password Widget then it would make more sense to try and re-use rather than just drop everything and start again. The end result is the same but we may be able to reduce the number of UI transactions.

It could well be that we could attach a 'TargetKey' when PerformLayout is used and store it as an attribute, OR, place something within the layout context.