Reinstated command concatenation.

Example:

    Abjad IDE - scores [examples]

       1: Blue Example Score (2013)
       2: Étude Example Score (2013)
       3: Red Example Score (2013)

          scores - copy (cp)
          scores - new (new)
          scores - remove (rm)
          scores - rename (ren)

    > red m 1

    Red Example Score (2013) - materials - instrumentation

       1: __init__.py
       2: __metadata__.py
       3: definition.py
       4: output.py
       5: versions/

          definition.py - autoedit (da)
          definition.py - check (dc)
          definition.py - open (do)
          definition.py - output (dp)

          output.py - check (oc)
          output.py - illustrate (oi)
          output.py - open (oo)

    >