imap-send: fix minor mistakes in the logs

imap-send: fix minor mistakes in the logs

Some minor mistakes have been found in the logs. Most of them include
error messages starting with a capital letter, and ending with a period.
Abbreviations like "IMAP" and "OK" should also be in uppercase. Another
mistake was that the error message showing unknown authentication
mechanism used was displaying the host rather than the mechanism in the
logs. Fix them.

Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>