Add 'human' date format

Add 'human' date format

This adds --date=human, which skips the timezone if it matches the
current time-zone, and doesn't print the whole date if that matches (ie
skip printing year for dates that are "this year", but also skip the
whole date itself if it's in the last few days and we can just say what
weekday it was).

For really recent dates (same day), use the relative date stamp, while
for old dates (year doesn't match), don't bother with time and timezone.

Also add 'auto' date mode, which defaults to human if we're using the
pager.  So you can do

	git config --add log.date auto

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

Note that this time format still shows the timezone for recent enough
events (but not so recent that they show up as relative dates).  You can
combine it with the "-local" suffix to never show timezones for an even
more simplified view.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Stephen P. Smith <ischis2@cox.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>