TEZ-1447. Provide a mechanism for InputInitializers to know about
Vertex state changes. (sseth)
(cherry picked from commit 9085e7bb4d3d9a5c1a91aac48048da8127cee17a)
Update CHANGES.txt for TEZ-1447
(cherry picked from commit 44e6a77cc5e6e09e97c5b1525428bf67967c1d25)