[PATCH] add context switch counters

[PATCH] add context switch counters

From: Peter Chubb <peterc@gelato.unsw.edu.au>

Currently, the context switch counters reported by getrusage() are
always zero.  The appended patch adds fields to struct task_struct to
count context switches, and adds code to do the counting.

The patch adds 4 longs to struct task struct, and a single addition to
the fast path in schedule().