revive Calendar::eventRangeToEventFootprints for constraint testing

src/Calendar.constraints.js

@@ -299,8 +299,9 @@ Calendar.prototype.eventRangesToEventFootprints = function(eventRanges) {
 	var eventFootprints = [];
 
 	for (i = 0; i < eventRanges.length; i++) {
-		eventFootprints.push(
-			eventRangeToEventFootprint(eventRanges[i])
+		eventFootprints.push.apply( // footprints
+			eventFootprints,
+			this.eventRangeToEventFootprints(eventRanges[i])
 		);
 	}
 
@@ -308,6 +309,11 @@ Calendar.prototype.eventRangesToEventFootprints = function(eventRanges) {
 };
 
 
+Calendar.prototype.eventRangeToEventFootprints = function(eventRange) {
+	return [ eventRangeToEventFootprint(eventRange) ];
+};
+
+
 /*
 Parses footprints directly.
 Very similar to EventDateProfile::parse :(