Task: allow Task to call AddSlave when running, only safe before flushing the first slave
Task: allow Task to call AddSlave when running, only safe before flushing the first slave

Also add an ASSERT in finish() for TASK_DONE state.

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