Unlike the current code, it does no looping to count days or do
table lookups, which means running time doesn't increase with year
or month. A good thing if it's call a lot, especially if the
algorithm were asked to compute dates centuries or more from the
epoch start.
As a bonus, handles negative time values.
Change-Id: I198a23daf621e40623e6b44dacf2387078b4db9c
Some drivers set tm_wday just fine and do not need it coerced to
be correct. Others set tm_yday, so don't overwrite what the driver
sets; just zero it inside if it can't fill the field. Move calls
to set_day_of_week() to the sorts of drivers that presumably
required the hammer (FS#11814) in get_time() where the weekday
isn't locked to the date.
Change-Id: Idd0ded6bfc9d9f48fcc1a6074068164c42fcf24a
