Bug 170668 [DataBinding] [Patch] Add SWTObservables.observeTooltipText()
Adds support for binding to SWT Control TooltipText property.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/internal/databinding/internal/swt/ControlObservableValue.java
* @param attribute
	 */
	public ControlObservableValue(Control control, String attribute) {
		super(control);
		this.control = control;
		this.attribute = attribute;
		if (!attribute.equals(SWTProperties.ENABLED)
				&& !attribute.equals(SWTProperties.VISIBLE)) {
			throw new IllegalArgumentException();
		}
	}
	public void doSetValue(Object value) {
		Object oldValue = doGetValue();
		if (attribute.equals(SWTProperties.ENABLED)) {
			control.setEnabled(((Boolean) value).booleanValue());
		} else if (attribute.equals(SWTProperties.VISIBLE)) {
			control.setVisible(((Boolean) value).booleanValue());
		}
		fireValueChange(Diffs.createValueDiff(oldValue, value));
	}
	public Object doGetValue() {
		boolean value = attribute.equals(SWTProperties.ENABLED) ? control
				.getEnabled() : control.getVisible();
		return value ? Boolean.TRUE : Boolean.FALSE;
	}
	public Object getValueType() {
		return Boolean.TYPE;
	}
}