Improve sed portability

Improve sed portability

The behaviour of "sed" on an incomplete line is unspecified by POSIX, and
On Solaris it apparently fails to process input that doesn't end in a LF.

Consequently constructs like

  re=$(printf '%s' foo | sed -e 's/bar/BAR/g' $)

cause re to be set to the empty string. Such a construct is used in
git-submodule.sh.

Because the LF at the end of command output are stripped away by the
command substitution, it is a safe and sane change to add a LF at the end
of the printf format specifier.

Signed-off-by: Chris Ridd <chris.ridd@isode.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>