Do some fairly major include file cleanups to further separate kernelland

Do some fairly major include file cleanups to further separate kernelland
from userland.

    * Do not allow userland to include sys/proc.h directly, it must use
      sys/user.h instead.   This is because sys/proc.h has a huge number
      of kernel header file dependancies.

    * Do cleanups and work in lwkt_thread.c and lwkt_msgport.c to allow
      these files to be directly compiled in an upcoming userland thread
      support library.

    * sys/lock.h is inappropriately included by a number of third party
      programs so we can't disallow its inclusion, but do not include
      any kernel structures unless _KERNEL or _KERNEL_STRUCTURES are
      defined.

    * <ufs/ufs/inode.h> is often included by userland to get at the
      on-disk inode structure.  Only include the on-disk components and do
      not include kernel structural components unless _KERNEL or
      _KERNEL_STRUCTURES is defined

    * Various usr.bin programs include sys/proc.h unnecessarily.

    * The slab allocator has no concept of malloc buckets.  Remove malloc
      buckets structures and VMSTAT support from the system.

    * Make adjustments to sys/thread.h and sys/msgport.h such that the
      upcoming userland thread support library can include these files
      directly rather then copy them.

    * Use low level __int types in sys/globaldata.h, sys/msgport.h,
      sys/slaballoc.h, sys/thread.h, and sys/malloc.h, instead of
      high level sys/types.h types, reducing include dependancies.