Bug 201042 [Accessibility]Chart scritp should not add by auto when click the down in keyboard[17]
Description: Chart scritp should not add by auto when click the down in keyboard[0704] Step: 1. New a chart and switch to script view. 2. Let the point on the script function selection. 3. Click the down on keyboard. Actual result: A function will add by auto. Expected result: Customer can not select the function under the second function by keyboard, and it should not be added by auto.
chart/org.eclipse.birt.chart.ui.extension/src/org/eclipse/birt/chart/ui/swt/composites/HeadStyleAttributeComposite.java
FillLayout flMain = new FillLayout();
		flMain.marginHeight = 0;
		flMain.marginWidth = 0;
		GridLayout glContent = new GridLayout();
		glContent.verticalSpacing = 5;
		glContent.horizontalSpacing = 5;
		glContent.marginHeight = 4;
		glContent.marginWidth = 4;
		glContent.numColumns = 6;
		this.setLayout(flMain);
		cmpContent = new Composite(this, SWT.NONE);
		cmpContent.setLayout(glContent);
		lblHeadStyle = new Label(cmpContent, SWT.NONE);
		GridData gdLHeadStyle = new GridData(
				GridData.HORIZONTAL_ALIGN_BEGINNING);
		lblHeadStyle.setLayoutData(gdLHeadStyle);
		lblHeadStyle.setText(Messages
				.getString("HeadStyleAttributeComposite.Lbl.HeadStyle")); 
		cmbHeadStyle = new HeadStyleChooserComposite(cmpContent, SWT.DROP_DOWN
				| SWT.READ_ONLY, laCurrent.getValue());
		GridData gdCBHeadStyle = new GridData(GridData.FILL_HORIZONTAL);
		gdCBHeadStyle.horizontalSpan = 5;
		cmbHeadStyle.setLayoutData(gdCBHeadStyle);
		cmbHeadStyle.addListener(this);
	}
	public void addListener(Listener listener) {
		vListeners.add(listener);
	}
	public void setLineDecorator(LineDecorator attributes) {
		laCurrent = attributes;