Make bsp safer to use.

Edit

1 Now it is copy-constructable.
2 Called no longer needs to reset itemDiscovered after call items.
Remove unnecessary note overlapping check and add Q_ASSERT instead
Fix too many tuplet voices (> VOICES)
Fix multiple voices for drum tracks
Fix !useMultipleVoices case for tied tuplets
Enclose assert functions by #ifdef QT_DEBUG
Remove incorrect comment
Add note overlap check after removeOverlappingNotes function
add QT_NO_DEBUG to release cflags
Merge pull request #616 from yufanyufan/patch-8

Make bsp safer to use.
Merge pull request #622 from trig-ger/midi_fixes

Fixes for MIDI import
adapt bsp changes
Merge branch 'master' of github.com:musescore/MuseScore
fix segment type in debugger; fix start repeat barline
add vtest for barlines
smufl: fix repeat barline dots