I will be updating the x86_64 backtrace code to search all of the
exception stacks for the origin of the active tasks' backtrace
when the info is not available in the dumpfile header.

Currently it first searches in the task's process stack, then the
per-cpu IRQ stack, and lastly the per-cpu NMI stack.  This patch
looks at all 3 exception stacks in 2.4 kernels (NMI, STACKFAULT
and DOUBLEFAULT), and all 5 exception stacks in 2.6 kernels
(NMI, STACKFAULT, DOUBLEFAULT, DEBUG and MCE).

The patch also removes an erroneous warning message re: the
task cpu not being the same as the IRQ or exception stack cpu
that gets displayed when doing a non-context-sensitive "bt -E",
again only on an x86_64.

Dave