Improved date support

[Sanjoy Mahajan]

>  5/1/99       (May 1 1999)

This format is ambiguous in an internationally used revision-control
system: 5/1/99 means 5 Jan 1999 in the U.K. (and probably much of
Europe), and means 1 May 1999 in the U.S. (and maybe Canada).

Having lived for many years at various ends of the formats, I've now
settled on YYYY-MM-DD, since it's almost self-documenting (and I'm
told is the standard in some countries).

-Sanjoy

`Never underestimate the evil of which men of power are capable.'
         --Bertrand Russell, _War Crimes in Vietnam_, chapter 1.