autostart next scene when rolling (issue #3)

modified:   LoopiditySDL.depend
modified:   jack_io.cpp
modified:   jack_io.h
modified:   loopidity.cpp
modified:   loopidity.h
modified:   scene.cpp
modified:   scene.h
modified:   scene_sdl.cpp
modified:   scene_sdl.h
modified:   trace.cpp
modified:   trace.h