Fix getting a calendar event list with Exchange 14.2.247.0

The SOAP query was returing the following error:

    The request failed schema validation: The 'EndDate' attribute is
    invalid - The value '2014-10-28' is invalid according to its
    datatype 'http://www.w3.org/2001/XMLSchema:dateTime' - The string
    '2014-10-28' is not a valid XsdDateTime value.

The fix is simply to use the DATETIME format instead of the DATE format,
as advised in the MSDN page of the CalendarView element.

http://msdn.microsoft.com/en-us/library/office/aa564515%28v=exchg.140%29.aspx

pyexchange/exchange2010/soap_request.py

@@ -116,8 +116,8 @@ def get_item(exchange_id, format=u"Default"):
   return root
 
 def get_calendar_items(format=u"Default", start=None, end=None, max_entries=999999):
-  start = start.strftime(EXCHANGE_DATE_FORMAT)
-  end = end.strftime(EXCHANGE_DATE_FORMAT)
+  start = start.strftime(EXCHANGE_DATETIME_FORMAT)
+  end = end.strftime(EXCHANGE_DATETIME_FORMAT)
 
   root = M.FindItem(
     {u'Traversal': u'Shallow'},