Bring boot2 and the loader into line with our new dual-console support.

Bring boot2 and the loader into line with our new dual-console support.
We now support dual-consoles by default with options to force either
video (-V) or serial port (-h).  Both boot2 and the loader now properly
parse the options/howto-flags.

Note that the kernel does not yet support dual consoles, but the loader
does tell the kernel which console to use based on which console was used
during the load stage (or the video console if no input was received from
any console during the load stage).