core: timing: add special handling of long frame intervals

core: timing: add special handling of long frame intervals

Add separate handling for the case where the time to flip the next
frame on the VO is more than 50 ms away. In that case don't update OSD
contents yet, but wait for possible changes until 50 ms before the
frame. Sleep until that time in mp_input_get_cmd(), so the sleep is
done in select() and input events can be responded to immediately.
Also raise the limit on audio out delay used to limit sleep.