pitch_squash_engraver broken in 2.11.22

[Bruce McIntyre]

> I'm not top posting.

%% pitch_squash_engraver is broken in 2.11.22
%% consequently \improvisationOn is broken

%% this is example from
%%http://lilypond.org/doc/v2.11/Documentation/user/lilypond/Improvisation#Improvisation
%% consider adding this to regression test?

\new Staff \with {
  \consists Pitch_squash_engraver
} \transpose c c' {
  e8 e g a a16(bes)(a8) g \improvisationOn
  e8
  ~e2~e8 f4 fis8
  ~fis2 \improvisationOff a16(bes) a8 g e
}