Wrote (!pwd) tests.

Current directory is now managed cleanly through all parts of the Score
Manager. This is done using TemporaryDirectoryChange context managers.

Example:

    Score manager - example scores

        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)

    > !pwd

    /Users/trevorbaca/Documents/abjad/scoremanager

    > red example score

    Red Example Score (2013)

        build (u)
        distribution (d)
        makers (k)
        materials (m)
        segments (g)
        stylesheets (y)

        score pdf - open (pdfo)

    > !pwd

    /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score

    > g

    Red Example Score (2013) - segments

        1: segment 01
        2: segment 02
        3: segment 03

        all segments - lilypond file - interpret (lyi)
        all segments - make module - interpret (mmi)
        all segments - pdf - open (pdfo)
        all segments - pdf - version (pdfs)

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

    > !pwd

    /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments

    > 1

    Red Example Score (2013) - segments - segment 01

        definition module - edit (dme)
        definition module - edit at top (dmE)

        make module - interpret (mmi)
        make module - read only (mmro)

        pdf - open (pdfo)
        pdf - version (pdfs)

    > !pwd

    /Users/trevorbaca/Documents/abjad/scoremanager/scores/red_example_score/segments/segment_01

    >

This commit adds (!pwd) tests for all concrete managers and concrete wranglers.