Customized autoeditor prompt.

Example:

    Red Example Score (2013) - materials - tempo inventory (EDIT)

       1: 8=72
       2: 8=108
       3: 8=90
       4: 8=135

          elements - add (add)
          elements - move (mv)
          elements - remove (rm)
          editing - done (done)

    |>

Note that the prompt is '|>' instead of just '>'.

The point is to provide passive reinforcement to the user that the autoeditor
environment differs slightly from the other environments in the IDE.