Bug 520530

Some profiling data (in a 768MB memory vmware, 1.9G Core 2 CPU):

If we set a MonthCalendar with CalendarDimensions = new Size(4,3)

and then click the prev month button, we will wait about 16 seconds to see the result.
about 6 seconds is consumed by RemoveChildren in MonthCalendarDataGridProvider.OnDateChanged,

about 9 seconds is consumed by AddChildren in 
MonthCalendarDataGridProvider.OnDateChanged,
and about the 9 seconds, in AddChildren:

		private void AddChildren ()
		{
			MonthCalendarListItemProvider item;
			SelectionRange range = calendar.GetDisplayRange (false);

			for (DateTime d = range.Start;
			     d <= range.End; d = d.AddDays (1)) {
				int days = (d - range.Start).Days;
				int r = (int)System.Math.Floor ((double)days
					/ (double)MonthCalendarProvider.DaysInWeek);
				int c = days - (r * MonthCalendarProvider.DaysInWeek);
				item = new MonthCalendarListItemProvider (
					this, calendarProvider, Control, d, r, c); //Line #A
				item.Initialize (); //Line #B
				AddChildProvider (false, item); //Line #C
				gridChildren.Add (d, item);
			}
			...
		}


Line A took 1 seconds， Line B took 3.5 seconds, Line C took 4.5 seconds. other lines of code took nearly no time.