SIGABORT when appending measures to score with linked staves
Context: commit b9984ffeaf, self-compiled under Ubuntu 11.10
1) Create a score with two linked staves: staves must be linked in the New Score Wizard
2) With "Create | Measures | Append measures", append some measures
*) The staff types do not matter: they may be the same type or different types.
*) Scores with a single staff or with multiple, non-linked staves are fine.
*) Scores with staves linked via the "Create | Instruments" menu after the initial creation do not show this issue (but show other problems)
*) Only happens when there are linked staves and the linking is done via the New Score Wizard.