There is a bug with git rebase -i --root when a fixup or squash line is
applied to the new root. We attempt to amend the commit onto which they
apply with git reset --soft HEAD^ followed by a normal commit. Unlike a
real commit --amend, this sequence will fail against a root commit as it
has no parent.
Fix rebase -i to use commit --amend for fixup and squash instead, and
add a test for the case of a fixup of the root commit.
Signed-off-by: Chris Webb <chris@arachsys.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>