Bug 208052 [Markers] Tasks does not sort by completion
Sorting by the completion currently does nothing.
bundles/org.eclipse.ui.ide/src/org/eclipse/ui/internal/provisional/views/markers/MarkerPriorityField.java
* 
	 * @see org.eclipse.ui.internal.provisional.views.markers.MarkerField#getColumnHeaderText()
	 */
	public String getColumnHeaderText() {
		return MarkerSupportConstants.EMPTY_STRING;
	}
	/* (non-Javadoc)
	 * @see org.eclipse.ui.internal.provisional.views.markers.api.MarkerField#getColumnTooltipText()
	 */
	public String getColumnTooltipText() {
		return MarkerMessages.priority_description;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.ui.internal.provisional.views.markers.api.MarkerField#getDefaultColumnWidth(org.eclipse.swt.widgets.Control)
	 */
	public int getDefaultColumnWidth(Control control) {
		return getHighPriorityImage().getBounds().width * 2;
	}
	/**
	 * Get the image for high priority
	 * 
	 * @return Image
	 */
	private Image getHighPriorityImage() {
		return MarkerSupportInternalUtilities
				.createImage(HIGH_PRIORITY_IMAGE_PATH);
	}
	/*