ChangeScreen2: Support [/] keys to navigate files in a cycle

When viewing the last file pressing ] takes the user up to the
change screen. Allow [ to return them to the last file, much as [
is an undo for an accidental ] between files.

Likewise allow ] to enter into the commit message.

Change-Id: Id1fac2cb0a34ecd87f2526400019bd65bd294186
3 files changed