Bug 188578 Add "displayColumnName" on TabularLevel
Add Property "displayColumnName" on TabbularLevel and corresponding APIs on handle. Property Type: expression.
model/org.eclipse.birt.report.model.tests/test/org/eclipse/birt/report/model/parser/TabularCubeParserTest.java
assertEquals( DesignChoiceConstants.DATE_TIME_LEVEL_TYPE_MONTH, level
				.getDateTimeLevelType( ) );
		assertEquals( 3.0, level.getIntervalRange( ), 0.00 );
		assertEquals( "Jan", level.getIntervalBase( ) ); 
		assertEquals( DesignChoiceConstants.LEVEL_TYPE_DYNAMIC, level
				.getLevelType( ) );
		iter = level.staticValuesIterator( );
		RuleHandle rule = (RuleHandle) iter.next( );
		assertEquals( "rule expression", rule.getRuleExpression( ) ); 
		assertEquals( "display expression", rule.getDisplayExpression( ) ); 
		rule = (RuleHandle) iter.next( );
		assertEquals( "rule expression2", rule.getRuleExpression( ) ); 
		assertEquals( "display expression2", rule.getDisplayExpression( ) ); 
		iter = level.attributesIterator( );
		LevelAttributeHandle attribute = (LevelAttributeHandle) iter.next( );
		assertEquals( "var1", attribute.getName( ) ); 
		assertEquals( DesignChoiceConstants.COLUMN_DATA_TYPE_STRING, attribute
				.getDataType( ) );
		attribute = (LevelAttributeHandle) iter.next( );
		assertEquals( "var2", attribute.getName( ) ); 
		assertEquals( DesignChoiceConstants.COLUMN_DATA_TYPE_INTEGER, attribute
				.getDataType( ) );
		
		iter1 = level.valueAccessControlsIterator( );
		ValueAccessControlHandle valueAccessControl = (ValueAccessControlHandle) iter1
				.next( );
		assertEquals( "level user1; level user2", valueAccessControl 
				.getPropertyHandle( IAccessControlModel.USER_NAMES_PROP )
				.getStringValue( ) );
		assertEquals( "level role1; level role2", valueAccessControl