Segfault on cyclic references in markup

[Rune Zedeler]

This clearly should go wrong, but I report it anyway because it 
segfaults, and segfaults are baaad :-)

\version "2.10.1"
\header {
  title = \markup \fromproperty #'header:title
}
\score {
  { c' d' e' f' }
}

-Rune