fix for need_resched from Ian Abbott <abbotti@mev.co.uk>:
This patch alters the Comedi driver's linux/sched.h compatibility header
to move the need_resched function after the #include_next directive.
This is because the 'current' task variable is not defined until after
the real linux/sched.h is included. I've also removed the comment - "/*
not sure exactly when need_resched() was added */"; I've checked, and it
was added in 2.4.20 as the code stated. I thought I'd fix the incorrect
comment at the top of the file while I was at it.