sequencer: notify user of --update-refs activity

sequencer: notify user of --update-refs activity

When the user runs 'git rebase -i --update-refs', the end message still
says only

  Successfully rebased and updated <HEAD-ref>.

Update the sequencer to collect the successful (and unsuccessful) ref
updates due to the --update-refs option, so the end message now says

  Successfully rebased and updated <HEAD-ref>.
  Updated the following refs with --update-refs:
	refs/heads/first
	refs/heads/third
  Failed to update the following refs with --update-refs:
	refs/heads/second

To test this output, we need to be very careful to format the expected
error to drop the leading tab characters. Also, we need to be aware that
the verbose output from 'git rebase' is writing progress lines which
don't use traditional newlines but clear the line after every progress
item is complete. When opening the error file in an editor, these lines
are visible, but when looking at the diff in a terminal those lines
disappear because of the characters that delete the previous characters.
Use 'sed' to clear those progress lines and clear the tabs so we can get
an exact match on our expected output.

Reported-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>