kernel - Fix panic when X11 intercepts console
* The kprintf() path was trying to acquire the tty_token. When called
from a hard code section without the token already held this can block
and thus will assert.
* When a console intercept is active we now only print to it if we can
acquire the tty_token non-blocking. And too bad otherwise. The
dmesg log will still get the whole of the output.
* Remove a recursive kprintf() in the clist code.
* Document the return value for lwkt_trytoken().
Reported-by: Johannes Hofmann <johannes.hofmann@gmx.de>