[doc] measurePosition example

[Erik Sandberg]

Hi,

At 5.3.9 Time administration

there is a misleading example:

     \set Score.measureLength = #(ly:make-moment 5 4)
     c1 c4
     c1 c4
     c4 c4
     \set Score.measurePosition = #(ly:make-moment -3 8)
     b8 b b
     c4 c1

This should be
     \set Score.measurePosition = #(ly:make-moment 7 8)
in order to get the bar numbering correct (in the current example, both the 
third and fourth bar is bar #3).

This is both in 2.4 and 2.5

Erik