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( ElementPropertyDefn prop, String memberName )
	{
		propDefn = prop;
		assert propDefn != null;
		assert propDefn.getTypeCode( ) == IPropertyType.STRUCT_TYPE;
		assert !propDefn.isList( );
		IPropertyDefn memberDefn = propDefn.getStructDefn( ).getMember(
				memberName );
		assert memberDefn != null;
		refType = PROPERTY_MEMBER;
		member[0] = (StructPropertyDefn) memberDefn;
		index[0] = -1;
		depth = 1;
	}
	/**
	 * Reference to a member of a top-level structure.
	 * <p>
	 * property.member
	 * 
	 * @param prop
	 *            the element property definition which is structure or
	 *            structure list type
	 * @param memberDef
	 *            the structure member definition of the element property
	 *            definition
	 */
	MemberRef( ElementPropertyDefn prop, StructPropertyDefn memberDef )
	{
		propDefn = prop;