================================================================
OTHER CHANGES IN RELEASE 10
================================================================
1.  Changed PAGING.C and other files to self-map page directory,
    which reduces the number of physical addresses used, and
    gives the page tables the same virtual address in each
    address space

2.  Reading screen size from BIOS data segment instead of VGA
    registers (KSTART.ASM temporarily maps page 0 to allow this)

3.  Changed semantics of disable() function to replace critb()

4.  Got rid of all volatile variable declarations -- they weren't
    needed and now I have fewer compiler warnings

5.  Got rid of curr_task as a parameter to many kernel functions;
    now using global variable _curr_task instead

6.  Added skeletal asm startup code for apps (USTART.ASM)

7.  Restored grim reaper (reclaims memory of dead tasks, now
    call 'buffy')

8.  Restored code to unmap discardable kernel memory
