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.
Adding tests that cover the two default formatters.

Tests now cover jQuery.format.date.defaultLongDateFormat and
jQuery.format.date.defaultShortDateFormat for a variety of input types.
Adds jwadhams as a contributor; Updates the README; Renames test variables