Bug 181121 Model should provide utility method for cube to get correspond dimension key.
In model cube handle, the relation of cube data set and dimension data sets are managed by a series of dimension condition handles.We need model to add utility method so that we can easily get corresponding dimension data set column names according to given cube dimension keys.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/MemberRef.java
index[1] = memberRef.index[1];
		depth = memberRef.depth;
	}
	/**
	 * Property (list, structure)
	 * 
	 * Reference to the top-level property list. Points to the first index
	 * within that list.
	 * 
	 * @param prop
	 *            the property definition
	 */
	MemberRef( ElementPropertyDefn prop )
	{
		propDefn = prop;
		assert propDefn != null;
		assert propDefn.getTypeCode( ) == IPropertyType.STRUCT_TYPE;
		refType = PROPERTY;
		index[0] = -1;
		depth = 1;
	}
	/**
	 * Reference to the nth item within the top-level property list.
	 * <p>
	 * property.list[n]
	 * 
	 * @param prop
	 *            the property definition
	 * @param n
	 *            the list index