be more specific (thanks Mark Morrissey)

from picirq.c and remove timer.c completely.  Update runoff.list.

updated copyright year

There is a potential memory leak when mappages() fails inside setupkvm().
A call to freevm() is added in this case so as to reclaim the lost mapping pages.

mycpu() in proc.c.

to find a per-cpu id with which we locate a cpu's cpu struct.

myproc() points to a different thread.

   myproc();
   sched();
   myproc();  // this proc maybe different than the one before sched

Thus, in a function that operates on one thread better to retrieve the
current process once at the start of the function.