Abstract out accesses to object hash array

Abstract out accesses to object hash array

There are a few special places where some programs accessed the object
hash array directly, which bothered me because I wanted to play with some
simple re-organizations.

So this patch makes the object hash array data structures all entirely
local to object.c, and the few users who wanted to look at it now get to
use a function to query how many object index entries there can be, and to
actually access the array.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>