rebase -i: make post-rewrite work for 'edit'

rebase -i: make post-rewrite work for 'edit'

The post-rewrite support, in the form of the call to
'record_in_rewritten', was hidden in the arm where we have to record a
new commit for the user.  This meant that it was never invoked in the
case where the user has already amended the commit by herself.

[The test is designed to exercise both arms of the 'if' in question.]

Furthermore, recording the stopped-sha (the SHA1 of the commit before
the editing) suffered from a cut&paste error from die_with_patch and
used the wrong variable, hence it never recorded anything.

Noticed by Junio.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>