Bug 138562 Splite extendsexcpetion to seperate sub class
The suggestion is Parent invalid Cycle extends Different type extends Not top level extends
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/DesignElement.java
try
		{
			checkExtends( parent );
		}
		catch ( ExtendsException e )
		{
			return false;
		}
		return true;
	}
	/**
	 * Checks the parent element.
	 * 
	 * @param parent
	 *            the parent element
	 * @throws ExtendsException
	 *             throws <code>ExtendsException</code> if the parent element
	 *             is <code>NOT_FOUND</code>,<code>WRONG_TYPE</code>,
	 *             <code>SELF_EXTEND</code>,<code>CIRCULAR</code>.
	 */
	public void checkExtends( DesignElement parent ) throws ExtendsException
	{
		String extendsName = getExtendsName( );
		IElementDefn defn = getDefn( );
		if ( parent == null )
		{
			throw new ExtendsException( this, extendsName,
					ExtendsException.DESIGN_EXCEPTION_NOT_FOUND );
		}
		else if ( parent.getDefn( ) != defn )