[illumos-Developer] webrev: add -R support to date

[Garrett D'Amore]

This webrev adds support for "-R" to date, which is useful for some
scripts designed for Linux that expect it to work.

Note that we match the Linux behavior precisely, rather than the Linux
"documented" behavior of RFC 822.

The webrev is here:  http://mexico.purplecow.org/gdamore/webrev/date-r/

For the record, this change will help Nexenta, which is why I'm pushing
it, but it may help other parties too. :-)

	- Garrett