[Cooker] beta3 install BUG : usbmouse and devfs

[Eric Fernandez]

Fresh install of beta 3, with a Logitech USB mouse optical + wheel.
That mouse is correctly detected at install, but is not working at boot. 
The /dev/usbmouse symbolic link is correctly created at boot, but it has 
not target. It points to dev/input/mouse0, but this file is missing. I 
run mousedrake at each boot, as root, to make it work.