Avoid uneccessare delegateable invalidation

When invalidating instances, each delegeteable in that instance is
invalidated. So there is no need to invalidate the parent delegateables
or the instance again.

I guess more optimization could be done here. This speed up proposal
creation by about 15x on my test installation.
Merge pull request #876 from xi/feature-avoid-uneccessary-invalidation

Avoid uneccessary delegateable invalidation