... Should have no effect on generated code, except perhaps some slight faster
virtual function calls. Mostly useful as documentation of design intent.
Tried to mark every one of our classes that inherits from another, or is a
base for others, or has abstract virtual functions, and a few others besides.
// I suggest that when this is no longer experimental, rather than all these #ifdef's,
// this be done by factoring, i.e., add two subclasses to MixerTrackCluster,
// MixerNoteTrackCluster and MixerWaveTrackCluster, such that all the common
// code is in the parent, and these #ifdef's are only around
// MixerNoteTrackCluster rather than sprinkled throughout MixerTrackCluster.
This bug was introduced in commit 10680 and caused in MixerTrackCluster::UpdatePan(), by using USE_MIDI (which is on in releases) instead of EXPERIMENTAL_MIDI_OUT (which is off). It checked whether a NoteTrack pointer was NULL, and if not, hid the Pan slider (not used in NoteTrack clusters). But an invalid pointer is non-null, so was causing the Pan slider to always be hidden.
