Fix type error in jsdate.js InLeapYear that led to bad calculations.

InLeapYear was passing the time in millis as an integer, which lead to
overflow errors and wrong results.

jsdate.c

@@ -107,7 +107,7 @@ static int YearFromTime(double t)
 	return y;
 }
 
-static int InLeapYear(int t)
+static int InLeapYear(double t)
 {
 	return DaysInYear(YearFromTime(t)) == 366;
 }