bitkeeper revision 1.1588 (42999d00gxHg_hThncByjrGk7labNA)

Tidy up and fix the bit-scanning operations. In particular,
find_{first,next}_[zero_]bit(addr, max) may return any value >= max
if no suitable bit is found. This is now also the case for first_cpu()
and next_cpu() (unlike Linux!). I don't believe that any callers
care -- they always check for >= NR_CPUS, and I fixed any_online_cpu()
separately. This reduces code size and will improve performance.
Signed-off-by: Keir Fraser <keir@xensource.com>