Bug 183579 Model need hold on DimensionConditionHandle and DimensionJoinConditionHandle signleton or overwrites the equals and hashcode method
The Dataset Joint Editor need join two Editparts which have the same model. But the DimensionConditionHandle and the DimensionJoinConditionHandle are create a new instance erery time when I get them. So model need hold on them signleton or overwrites the equals and hashcode method.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/core/MemberRef.java
*/
	MemberRef( MemberRef memberRef )
	{
		refType = memberRef.refType;
		propDefn = memberRef.propDefn;
		member[0] = memberRef.member[0];
		member[1] = memberRef.member[1];
		index[0] = memberRef.index[0];
		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;
	}
	/**