"Continue boot" will now be disabled if there are no boot volumes.
Also, there will be an additional menu item "Reboot" in that case.
The boot device menu will now show a disabled "No boot devices found" label
then, and will be selected upon entry. Added a help text to "Rescan volumes"
which will also be selected upon entry if there is no boot device.
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@8649 a95241bf-73f2-0310-859d-f6bbb57e9c96