jQuery.format.date.defaultLongDateFormat changed to use 24-hour time

The old jQuery.format.date.defaultLongDateFormat used two-digit 12-hour
time, but had no "am/pm" marker, which made it ambiguous.  Switching to
two-digit 24-hour time, which isn't ambigious, doesn't make the result
string longer, and is compatible with (among other things) MySQL
datetime formatting.