Bug 195335 Multithreads issue
a static hashmap in class HTMLServerImageHandler has not been synchronized which may leads to that the same images are handled(eg: write to disk) multiple times.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/HTMLServerImageHandler.java
* 
	 * @see org.eclipse.birt.report.engine.api2.IHTMLImageHandler#onFileImage(org.eclipse.birt.report.engine.api2.IImage,
	 *      java.lang.Object)
	 */
	public String onFileImage( IImage image, Object context )
	{
		return handleImage( image, context, "file", true ); 
	}
	/**
	 * handles an image report item and returns an image URL
	 * 
	 * @param image
	 *            represents the image design information
	 * @param context
	 *            context information
	 * @param prefix
	 *            image prefix in URL
	 * @param needMap
	 *            whether image map is needed
	 * @return URL for the image
	 */
	protected String handleImage( IImage image, Object context, String prefix,
			boolean needMap )
	{
		String mapID = null;
		if ( needMap )
		{
			mapID = getImageMapID( image );
			if ( map.containsKey( mapID ) )
			{