optimized gDrawLine() further  -->  5% speedup
optimized gDrawLine() further  -->  5% speedup

sklnet/DirectFB,kevleyski/directfb,dfbdok/DirectFB1,djbclark/directfb-core-DirectFB,lancebaiyouview/DirectFB,kaostao/directfb,kevleyski/DirectFB-1,kevleyski/DirectFB-1,lancebaiyouview/DirectFB,dfbdok/DirectFB1,Distrotech/DirectFB,deniskropp/DirectFB,djbclark/directfb-core-DirectFB,sklnet/DirectFB,kaostao/directfb,lancebaiyouview/DirectFB,sklnet/DirectFB,jcdubois/DirectFB,Distrotech/DirectFB,DirectFB/directfb,kevleyski/DirectFB-1,kevleyski/directfb,DirectFB/directfb,deniskropp/DirectFB,mtsekm/test,deniskropp/DirectFB,kevleyski/directfb,kevleyski/DirectFB-1,Distrotech/DirectFB,dfbdok/DirectFB1,jcdubois/DirectFB,deniskropp/DirectFB,mtsekm/test,djbclark/directfb-core-DirectFB,djbclark/directfb-core-DirectFB,jcdubois/DirectFB,kevleyski/directfb,lancebaiyouview/DirectFB,kaostao/directfb,sklnet/DirectFB,mtsekm/test,DirectFB/directfb