merge(s): apply consistent punctuation to "up to date" messages

merge(s): apply consistent punctuation to "up to date" messages

Although the various "Already up to date" messages resulting from merge
attempts share identical phrasing, they use a mix of punctuation ranging
from "." to "!" and even "Yeeah!", which leads to extra work for
translators. Ease the job of translators by settling upon "." as
punctuation for all such messages.

While at it, take advantage of printf_ln() to further ease the
translation task so translators need not worry about line termination,
and fix a case of missing line termination in the (unused)
merge_ort_nonrecursive() function.

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>