Avoid changing the buffer in no-op refactoring steps
Avoid changing the buffer in no-op refactoring steps

This reduces the undo size and doesn't set the buffer modification
flag unnecessarily.

rgrinberg/merlin,ocaml/merlin,ocaml/merlin,the-lambda-church/merlin,ocaml/merlin,dra27/merlin,dra27/merlin,ocaml/merlin,rgrinberg/merlin,rgrinberg/merlin,rgrinberg/merlin,the-lambda-church/merlin,dra27/merlin,dra27/merlin,the-lambda-church/merlin