Ambitus uses lexicographical order instead of pitch height

[Rune Zedeler]

Pitches are lexicographically ordered by octave, pitch, alteration.
This means that i.e. even though eis is a higher pitch than fes, it is 
lexicographically smaller. And because the ambitus engraver uses the 
lexicographical order to find the ambitus, it would prefer fes over eis 
as the top of the ambitus.

\version "2.10.25"
\score {
  \new Voice \with { \consists "Ambitus_engraver" } {
    \clef F c eis fes
}
}

-Rune