dispose of temp-files when using StreamingXlsx in XlsxEmitter #1533 (#…

…1535)

* dispose of temp-files when using StreamingXlsx in XlsxEmitter #1533

* revert back to old casting-mechanism

engine/uk.co.spudsoft.birt.emitters.excel/src/uk/co/spudsoft/birt/emitters/excel/ExcelEmitter.java

@@ -23,6 +23,7 @@
 import java.net.URL;
 
 import org.apache.poi.ss.usermodel.Workbook;
+import org.apache.poi.xssf.streaming.SXSSFWorkbook;
 import org.eclipse.birt.core.exception.BirtException;
 import org.eclipse.birt.report.engine.api.IRenderOption;
 import org.eclipse.birt.report.engine.content.IAutoTextContent;
@@ -342,6 +343,9 @@ public void end(IReportContent report) throws BirtException {
 					log.debug("ex:", ex.toString());
 				}
 			}
+			if (handlerState.getWb() instanceof SXSSFWorkbook) {
+				((SXSSFWorkbook) handlerState.getWb()).dispose();
+			}
 			handlerState = null;
 			reportOutputFilename = null;
 			reportOutputStream = null;