A bug in event-listener.ly

[Richard Shann]

While developing a Playback View in Denemo (music plays back while
LilyPond-typeset SVG is animated, building on Mathieu Demange's work) I
came across a bug in event-listener.ly:

In this procedure

#(define (format-tempo engraver event)
   (print-line engraver
               "tempo"
               ; get length of quarter notes, in seconds
               (/ (ly:event-property event 'metronome-count)
                   (format-moment (ly:duration-length (ly:event-property
                                                       event
                                                       'tempo-unit))))))

The division should be a multiplication, otherwise \tempo Presto 4=480
and \tempo Presto 2=240 result in different tempi being written out.

Richard