Fix getPitches(direction=DESCENDING) returning ascending scales

[jacobtylerwalls]

Before:

>>> c_maj = scale.MajorScale('C')
>>> c_maj.getPitches(direction=scale.Direction.DESCENDING)
[<music21.pitch.Pitch C5>, <music21.pitch.Pitch B4>, <music21.pitch.Pitch A4>, <music21.pitch.Pitch G4>, <music21.pitch.Pitch F4>, <music21.pitch.Pitch E4>, <music21.pitch.Pitch D4>, <music21.pitch.Pitch C4>]
>>> c_maj.getPitches(direction=scale.Direction.DESCENDING)
[<music21.pitch.Pitch C4>, <music21.pitch.Pitch D4>, <music21.pitch.Pitch E4>, <music21.pitch.Pitch F4>, <music21.pitch.Pitch G4>, <music21.pitch.Pitch A4>, <music21.pitch.Pitch B4>, <music21.pitch.Pitch C5>]

Two commits:

• 3e16218 fixes a more esoteric problem that I expected would help in some way,
• but it turned out that just 3cf3fa0 fixes what brought me here.

Tests for both.

[coveralls]

Coverage increased (+0.001%) to 93.049% when pulling 110802e on cache-scale into 0d3d7b1 on master.

[mscuthbert]

Thank you! Wonderful fix.