Bug 126527 [Field Assist] - API - Field Decoration alignment issues are different for cell editors
bundles/org.eclipse.jface/src/org/eclipse/jface/fieldassist/DecoratedField.java
* If there is currently a hover visible, the hover's text will be replaced
	 * with the specified text.
	 * 
	 * @param text
	 *            the text to be shown in the info hover, or <code>null</code>
	 *            if no text should be shown.
	 */
	public void showHoverText(String text) {
		showHoverText(text, control);
	}
	/**
	 * Hide any hover popups that are currently showing on the control.
	 * Normally, a decoration's description text will be shown in an info hover
	 * over the field's control as long as the mouse hovers over the decoration,
	 * and will be hidden when the mouse exits the control. This method can be
	 * used to hide a hover that was shown using <code>showHoverText</code>,
	 * or to programatically hide the current decoration hover.
	 * 
	 * <p>
	 * This message has no effect if there is no current hover.
	 * 
	 */
	public void hideHover() {
		if (hover != null) {
			hover.setVisible(false);
		}
	}
	/*
	 * The target control gained focus. Any decorations that should show only
	 * when they have the focus should be shown here.