RehearsalMark padding bug

[David Bobroff]

The following illustrates a bug with RehearsalMark padding.  With the
padding line commented out there is no problem.  When the padding is set
to more than 1 the elements of the rehearsal mark do not all move at the
same rate.  The bottom of the box around the Mark moves more than the
other elements.  When the padding is set to 3 as in the example below
the bottom of the box is pushed up higher than the crossbar on the 'A'
and the 'A' starts to poke through the top of the box.

-David

\book{
    \score {
        \notes \relative c'' {
            \override Score.RehearsalMark  #'print-function =
            #(make-stencil-boxer 0.1 0.25 0.25 Text_item::print)
            \override Score.RehearsalMark #'padding = #3
            c d e f 
            \mark "A"
            g a b c
            }
    }
}