Fix a reboot hang

Some IBM servers (IBM eServer xSeries 346, *cough*) do not reboot properly when issuing the “shutdown -r now” command; the server hangs after processing the last of the rc scripts. To mitigate this problem, append “reboot=b” to the kernel line in /boot/grub/grub.conf. This parameter tells the kernel to use the BIOS reboot function for the reset. This should allow the server to reboot successfully.