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 report document name.
	 */
	public static final String PARAM_REPORT_DOCUMENT = "__document"; 
	/**
	 * URL parameter name that gives the format to display the report, html or
	 * pdf.
	 */
	public static final String PARAM_FORMAT = "__format"; 
	/**
	 * Format parameter constants to display the report in html.
	 */
	public static final String PARAM_FORMAT_HTM = "htm"; 
	public static final String PARAM_FORMAT_HTML = "html"; 
	/**
	 * Format parameter constants to display the report in pdf.
	 */
	public static final String PARAM_FORMAT_PDF = "pdf"; 
	/**
	 * URL parameter name that gives the locale.
	 */
	public static final String PARAM_LOCALE = "__locale"; 
	/**
	 * URL parameter name that determins to support the SVG or not.
	 */
	public static final String PARAM_SVG = "__svg"; 
	/**
	 * URL parameter name that gives the page number to display the report.
	 */
	public static final String PARAM_PAGE = "__page"; 
	/**