[LilyPond] Support for drums

Steps to reproduce:
1. Open attached file: "Drum.mscz"
2. File > Save As...
3. Choose LilyPond format, and click Save

Expected behavior: MuseScore should export a proper drum staff to ensure correct appearance in the final PDF. I couldn't work out the correct code using \context command (the current layout of exported LilyPond files), but from what I understand it should involve use of \drummode, DrumVoice, and DrumStaff. For official documentation see http://lilypond.org/doc/v2.12/Documentation/user/lilypond/Common-notati…

Actual behavior: MuseScore currently exports the drum staff as pitched staff and the notes appear way below the staff in the final PDF:

...
ADrmvoiceAA = \relative c{
    \set Staff.instrumentName = #"Drumset"
    \set Staff.shortInstrumentName = #"Drm."
    \clef percussion
    %staffkeysig
    \key c \major 
    %bartimesig: 
    \time 4/4 
    r4 cis, r cis \bar "|."     | % 1
    R1 \bar "|." 
}% end of last bar in partorvoice
...

MuseScore version: 1.0 stable

(Operating System: Windows 7)