rollback: avoid retyping last chunk if it did not change
rollback: avoid retyping last chunk if it did not change

dra27/merlin,fxfactorial/merlin,rgrinberg/merlin,rgrinberg/merlin,dra27/merlin,the-lambda-church/merlin,ocaml/merlin,chriskonstad/merlin,the-lambda-church/merlin,haselwarter/merlin,chriskonstad/merlin,ocaml/merlin,chambart/merlin,haselwarter/merlin,haselwarter/merlin,chambart/merlin,fxfactorial/merlin,rgrinberg/merlin,fxfactorial/merlin,rgrinberg/merlin,haselwarter/merlin,dra27/merlin,ocaml/merlin,chambart/merlin,neojski/merlin,ocaml/merlin,chambart/merlin,dra27/merlin,neojski/merlin,fxfactorial/merlin,the-lambda-church/merlin,neojski/merlin,neojski/merlin