cleanup: rename key and item_head accessors to more friendly names

This patch does a quick search and replace:
B_N_PITEM_HEAD() -> item_head()
B_N_PDELIM_KEY() -> internal_key()
B_N_PKEY() -> leaf_key()
B_N_PITEM() -> item_body()

And the item_head version:
B_I_PITEM() -> ih_item_body()
I_ENTRY_COUNT() -> ih_entry_count()

And the treepath variants:
get_ih() -> tp_item_head()
PATH_PITEM_HEAD() -> tp_item_head()
get_item() -> tp_item_body()

... which makes the code much easier on the eyes.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>

reiserfscore/node_formats.c

@@ -842,7 +842,7 @@ void for_every_item(struct buffer_head *bh, item_head_action_t action,
 	struct item_head *ih;
 	item_action_t iaction;
 
-	ih = B_N_PITEM_HEAD(bh, 0);
+	ih = item_head(bh, 0);
 	for (i = 0; i < get_blkh_nr_items(B_BLK_HEAD(bh)); i++, ih++) {
 		if (action)
 			action(ih);