Material output illustration (oi) now implements artifact candidacy.

Example:

    Red Example Score (2013) - materials - tempo inventory

        * 8=72
        * 8=108
        * 8=90
        * 8=135

       1: __init__.py
       2: __metadata__.py
       3: definition.py
       4: illustration.ly
       5: illustration.pdf
       6: output.py
       7: versions/

          definition.py - autoedit (da)
          definition.py - check (dc)
          definition.py - edit (de)
          definition.py - output (dp)

          illustration.ly - edit (ie)
          illustration.ly - interpret (ii)
          illustration.pdf - open (io)

          output.py - check (oc)
          output.py - edit (oe)
          output.py - illustrate (oi)

    > oi
    The PDFs ...
        /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/tempo_inventory/illustration.candidate.pdf
        /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/tempo_inventory/illustration.pdf
    ... compare the same.
    Preserved /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/materials/tempo_inventory/illustration.pdf.

    >