Changes:

- implemented 'zone chains' zonelist_t and gfp_mask indexed zonelists[]
  speedups (Linus' idea) to handle fallback zones. This should enable
  advanced NUMA-style allocations as well. [fallback to different CPUs is 
  possible via changing build_zonelists().]

- <=16MB RAM boxes should boot just fine now.

- added page->zone for easier deallocation and generic cleanliness. This
  also helps NUMA.

- cleaned up the page-allocator namespace, there are only two 'core'
  page-allocation functions left: __alloc_pages() and __free_pages_ok().

- modules should compile again.

- we are now inlining the 'put_page_testzero()' part of __free_page_ok.
  This is subtle as page->count for reserved pages is now 'rotating' -
  this is fine though and lets us to put the rare PageReserved() branch
  into __free_page_ok().

- cleaned up pgtable.h, split into lowlevel and highlevel parts, this
  fixes dependencies in mm.h & misc.c.

- serial.c didnt clear freshly allocated bootmem - as a result now all
  bootmem allocations are explicitly cleared, it's not performance
  critical anyway.

- fixed code,data,initmem reporting.

- fixed boot task's swapper_pg_dir clearing

comments, reports welcome.

-- mingo