Day TH's: scope=col. Closes gh-1074

A TH must feature a way to know which span of TD's it applies to, and in simple tables such as date tables, this can be achieved through the use of the scope attribute.

ui/jquery.ui.datepicker.js

@@ -1721,7 +1721,7 @@ $.extend(Datepicker.prototype, {
 				thead = (showWeek ? "<th class='ui-datepicker-week-col'>" + this._get(inst, "weekHeader") + "</th>" : "");
 				for (dow = 0; dow < 7; dow++) { // days of the week
 					day = (dow + firstDay) % 7;
-					thead += "<th" + ((dow + firstDay + 6) % 7 >= 5 ? " class='ui-datepicker-week-end'" : "") + ">" +
+					thead += "<th scope='col'" + ((dow + firstDay + 6) % 7 >= 5 ? " class='ui-datepicker-week-end'" : "") + ">" +
 						"<span title='" + dayNames[day] + "'>" + dayNamesMin[day] + "</span></th>";
 				}
 				calender += thead + "</tr></thead><tbody>";