Tall system makes 2.13.26 give other systems too much vertical space

[Richard Sabey]

> I am not top-posting.

% If the music has at least one tall system and many vertically-short systems,
% v.2.13.26 gives the vertically-short systems too much vertical space.
% When using Feta font size 20 and A4 paper, Lilypond v.2.13.26 lays this
% example out on 4 pages, 4 systems per page. This is needlessly many pages:
% Lilypond should not need more than 2 pages.
% Proof: the music is one tall 4/4 bar followed by 112 short bars. Add the line 
% showLastLength = R1*112
% This omits only the first bar. and v.2.13.26 lays the music out on 2 pages
% with 10 staves on page 1. 

\version "2.13.26"

% showLastLength = R1*112 % uncomment this line to omit the first bar

\paper
{
        ragged-last-bottom      = ##f
}

rhMusic =
{
    << d'''4^\f \\ f'4_\f >>
    \repeat unfold 451 f'
}

lhMusic =
{
    \clef bass
    << f'4^\f \\ g,,4_\f >>
    \repeat unfold 451 g
}

pedalling =
{
    \set Staff.pedalSustainStyle = #'bracket
    s4\sustainOn s2.\sustainOff
}

\score
{
    \new PianoStaff
    <<
        \new Staff << \rhMusic >>
        \new Staff << \lhMusic \pedalling >>
    >>
    \layout { }
}