When a file is added in one commit and then edited in another, we were

incorrectly showing that file as edited when viewing commit ranges. The

problem here was that we weren't propagating the new-file state through

when the ancestor list included adding the file.

Ran unit tests. Newly-added test failed before the fix and succeeds

  after.
Posted a change that involved a bunch of commits where some files were

  added in one commit and then changed in later ones. Saw that commit

  range diffs properly showed the file as added when the selected base

  commit was the commit which added the file or earlier.