Performs the wrapup action for all of the active graphics devices,
leaving S-PLUS with no active graphics devices.
USAGE:
graphics.off()
SIDE EFFECTS:
This function executes the wrapup action for all of the currently
active graphics device.
This is important for flushing buffers, etc.
After execution, S-PLUS is in the same state as when it is first started,
i.e., there are no active graphics devices.
DETAILS:
This function iteratively calls
dev.off, which performs the actual
shutdown action one device at a time.