Modify the header of arch-update.py so that when using `bumblebee-status
-l modules`, the content of arch-update and batter-upower will be
separated (i.e., one more blank line between the doc of arch-update and
battery-upower).
This was causing an ocassional crash in bumblebee/engine.py threshold_state
when checkupdates fails, perhaps due to wifi not being up yet.
For me this showed up regularly on login.
