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.

As x86-64 is a superset of x86, we can use qemu-system-x86_64 to run
the OS image.

Signed-off-by: Antonio Gutierrez <chibby0ne@gmail.com>

switchuvm() is supposed to switch the TSS and page table to the
process p it is passed. Alas, instead of using p to access the
kstack field, it used the global proc. This worked fine because
(a) most uses of switchuvm() pass proc anyway and (b) because in
the schedule, where we call switchuvm with the newly scheduled
process, we actually set the global proc before the call. But I
think it's still a bug, even if it never broke a test case. :-)

Since readi() returns -1 for errors, checking with < against an unsigned
value is inadvisable. Checking with != works as intended however.

when a zero PDE is encountered while searching for present PTEs to free,
resume searching at first entry of the next page table instead of the
current entry of the next page table.

On platforms with NaCl support, ld.gold -V will return a "elf_i386_nacl" in
addition to "elf_i386", which will make the build fail.