reiserfs: balance_leaf refactor, format balance_leaf_new_nodes_paste

Break up balance_leaf_paste_new_nodes into:
balance_leaf_paste_new_nodes_shift
balance_leaf_paste_new_nodes_shift_dirent
balance_leaf_paste_new_nodes_whole

and keep balance_leaf_paste_new_nodes as a handler to select which
is appropriate.

Also reformat to adhere to CodingStyle.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Jan Kara <jack@suse.cz>