format modifiers that are needed for a 1003.2 compliant date(1). The
modifiers don't actually do anything at present and are not documented.
It's too confusing to the user to describe localization features when
they aren't implemented yet. It is safe to do this, as the modifiers
fall back to the default behavior if the locale doesn't support alternate
eras or numeric formats.
But, in anticipation of _some_ locale support, all month and day names and
abbrevs, certain time formats, am/pm, etc. are now accessed through variables.
