special console handling

[Clint Byrum]

In this bug report that I raised against upstart in Ubuntu, I suggest
(at the urging of Oliver Grawert and Emmet Hikory) that we add a job to
the upstart package which starts a serial console if the kernel has been
asked to start a serial console.

https://bugs.launchpad.net/ubuntu/+source/upstart/+bug/702574

Scott recommended in the merge proposal attached there that we discuss
how upstart can provide console handling rather than leaving it all to a
job file.

As I read it, the kernel has been patched to provide kernel arguments as
environment variables if they are specified as  foo=bar. So
console=ttyS0,38400 would end up as an environment varialble "console"
with the value of "ttyS0,38400", for init only.

I've given this some thought, and I was thinking maybe we could have
upstart fire an event:

console-redirected

Which could then be used for, say, the serial port case:

start on console-redirected CONSOLE_TTY=ttyS* and filesystem

exec getty /dev/$CONSOLE_TTY $CONSOLE_ARGS

Thoughts?