Bug 176681 Issue about creating context-parameter path in read-only path[0601]
Description: Issue about creating context-parameter path in read-only path Build number:2.2.0.v20070308 Steps to reproduce: 1. Deploy birt. 2. Set BIRT_VIEWER_DOCUMENT_FOLDER/BIRT_VIEWER_IMAGE_DIR/.. to a read-only path. 3. Preview report. Expected result: Because the path is read-only, folders should be created in ${java.io.tmpdir} Actual result: No folders are created in ${java.io.tmpdir} and reports cannot be previewed in frameset mode.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/utility/ParameterAccessor.java
* URL parameter name that gives the bookmark expression.
	 */
	public static final String PARAM_BOOKMARK = "__bookmark"; 
	/**
	 * URL parameter name that gives that image rtl option.
	 */
	public static final String PARAM_RTL = "__rtl"; 
	/**
	 * URL parameter name that gives the preview max rows option.
	 */
	public static final String PARAM_MAXROWS = "__maxrows"; 
	/**
	 * URL parameter name that gives the reportlet id.
	 */
	public static final String PARAM_INSTANCEID = "__instanceid"; 
	/**
	 * URL parameter name to indicate whether need to run a reportlet.
	 */
	public static final String PARAM_ISREPORTLET = "__isreportlet";
	/**
	 * URL parameter name to indicate the export encoding.
	 */
	public static final String PARAM_EXPORT_ENCODING = "__exportEncoding";
	/**
	 * Indentify the display text of select parameter
	 */
	public static final String PREFIX_DISPLAY_TEXT = "__isdisplay__"; 
	/**
	 * Indentify the parameter value is a locale string
	 */