[plt-scheme] date header for mail messages

Matthew Flatt wrote:
> > I looked at the `date' library in MzLib, but I couldn't find a date
> > format that matched RFC822's. 
> 
> It's now there as display format 'rfc822.

RFC822 has been obsoleted by RFC2822, which was 
promulgated in 2001.

In RFC822, years were given as two digits, although
all mail agents understand four digits.  In RFC2822,
four digits are specified, although two digits are 
allowed.  

So if the format gives years as four digits, it's 
more accurately described as 'rfc2822.

-- Paul