[PATCH RFC] cpu alloc cleanups and implementation improvement

[Rusty Russell <rusty@rustcorp.com.au>]

Hi all,

  I've argued with Christoph that his implementation contains gratuitous 
obsolescence of perfectly-good APIs; hopefully providing real patches will 
give us a more useful debate.

  It's in easy stages.  There are three general cleanup patches, then four 
patches to expose the current module percpu allocator as a the general dynamic 
percpu allocator, then documentation, a new __get_cpu_ptr() primitive and 
finally a test patch.

I hope this adds some light,
Rusty.