Transposing a score shouldn't transpose a drum staff

Steps to reproduce bug
1. Open Transpose Drums.mscz
2. Select entire score for transposition
3. Change to C-Sharp Major.

Expected result: Only instruments with pitch are transposed.
Actual result: Drum notes change.

MuseScore version: 0.9.6.3 stable

(Operating System: Windows 7)

first reported by chen lung: http://musescore.org/en/node/7869