fundamentally alter how we compute frames_per_beat(). this follows much discussion...

fundamentally alter how we compute frames_per_beat(). this follows much discussion on IRC. fundamentally, tempo and ONLY tempo affects the computation of frames_per_beat(), meter has no effect at all. However, following typical DAW conventions, we continue to want the "grid" to show metric divisions, not fixed beats, so add a new method (Meter::frames_per_division()) that retains the old math which takes meter into account. This commit will alter the behaviour of MIDI notes in any session with multiple time signatures. They will likely break. Unfortunately, there is no alternative to this breakage at this time.

git-svn-id: svn://localhost/ardour2/branches/3.0@10988 d708f5d6-7413-0410-9779-e7cbd77b26cf