Fix assert on wxCalendarCtrl creation under Windows 7.

Fix assert on wxCalendarCtrl creation under Windows 7.

Unlike previous versions of Windows, 7 includes the time component in the
return value of MonthCal_GetCurSel() and because of it the comparison with
m_date (which doesn't have any time part) fails.

Fix this by comparing just the date parts of the two wxDateTime objects.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63560 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775