This patch makes UML produce error messages instead of silently exiting
when one of several configuration mistakes are made.  FD_CHAN is now
mandatory so that people don't turn it off and complain about no boot
messages.

Some printks were turned into printfs in the tt mode gdb code so that they
appear on the screen.
Signed-off-by: Jeff Dike <jdike@addtoit.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>