userdiff style: normalize pascal regex declaration

userdiff style: normalize pascal regex declaration

Declare the pascal pattern consistently with how we declare the
others, not having "\n" on one line by itself, but as part of the
pattern, and when there are alterations have the "|" at the start, not
end of the line.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>