Replace the proposed 'auto' mode with 'auto:'

Replace the proposed 'auto' mode with 'auto:'

In addition to adding the 'human' format, the patch added the auto
keyword which could be used in the config file as an alternate way to
specify the human format.  Removing 'auto' cleans up the 'human'
format interface.

Added the ability to specify mode 'foo' if the pager is being used by
using auto:foo syntax.  Therefore, 'auto:human' date mode defaults to
human if we're using the pager.  So you can do

	git config --add log.date auto:human

and your "git log" commands will show the human-legible format unless
you're scripting things.

Signed-off-by: Stephen P. Smith <ischis2@cox.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>