Reduce title height by 2 pixels for theme "slick".

themes/slick/title-1-active.xpm

themes/slick/title-1-inactive.xpm

themes/slick/title-2-active.xpm

themes/slick/title-2-inactive.xpm

themes/slick/title-3-active.xpm

themes/slick/title-3-inactive.xpm

themes/slick/title-4-active.xpm

themes/slick/title-4-inactive.xpm

themes/slick/title-5-active.xpm

themes/slick/title-5-inactive.xpm

themes/slick/top-left-active.xpm

themes/slick/top-left-inactive.xpm

themes/slick/top-right-active.xpm

themes/slick/top-right-inactive.xpm