Since commit 376ccb8cbb453343998e734d8a1ce79f57a4e092 (rebase -i: style
fixes and minor cleanups), unchanged SHA-1s are no longer mapped via
$REWRITTEN. But the updating phase was not prepared for the old head
not being rewritten.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>