Bug 188052 Enhance the behavior of DimensionConditionHandle
Current in model implementation, there could be multiple DimensionConditionHandle corresponding to one dimension. This will cause problem for both UI and DtE. What we expect is that for each dimension, there are only one DimensionConditionHandle accompany with. Model should merge all the duplicate DimensionConditionHandle so that when UI/DtE is using model API the we can get unique DimensionConditionHandle for each dimension.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/olap/TabularCubeHandle.java
*/
	public DimensionConditionHandle addDimensionCondition(
			DimensionCondition condition ) throws SemanticException
	{
		PropertyHandle propertyHandle = getPropertyHandle( DIMENSION_CONDITIONS_PROP );
		return (DimensionConditionHandle) propertyHandle.addItem( condition );
	}
	/**
	 * Adds a dimension condition to the specified position.
	 * 
	 * @param condition
	 * @param posn
	 * @return the added dimension condition handle if succeed
	 * @throws SemanticException
	 */
	public DimensionConditionHandle addDimensionCondition(
			DimensionCondition condition, int posn ) throws SemanticException
	{
		PropertyHandle propertyHandle = getPropertyHandle( DIMENSION_CONDITIONS_PROP );
		return (DimensionConditionHandle) propertyHandle.insertItem( condition,
				posn );
	}
	/**
	 * Gets the iterator of the join conditions. Each one in the iterator is
	 * instance of <code>StructureHandle</code>.
	 * 
	 * @return iterator of the join conditions in this cube
	 */
	public Iterator joinConditionsIterator( )
	{