All commands the user gives interactively are copied to a backup-file. This
requires the -b option, or the assignment of TVback.

This file can be used (possibly after editing) to replay an edit-session,
as long as the input-file(s) were not yet overwritten. It is also a very
easy way of creating command-files: perform the edit manually, and use
the TVback-file to repeat it on different input-files.

The backup-file remains consistent after insert- or overstrike mode
was used. Such changes are translated into command sequences that would
have caused those same changes.

NOTE: Quite a number of actions make the backup-file impossible to play
      back. The most obvious ones are:
      - A loop terminated by CTRL_G will only show up as the loop in
        the backup-file - the termination is not registered.
      - Overwriting an input-file.
      - Using a different TVini-file during the re-run.
      - Using window resizing.