Several AFFS fixes.

	Several AFFS fixes.

	* grub-core/fs/affs.c (grub_affs_bblock): Replace flags with version.
	(GRUB_AFFS_FLAG_FFS): Removed.
	(GRUB_AFFS_SYMLINK_SIZE): Likewise.
	(GRUB_AFFS_FILETYPE_DIR): Make positive and unsigned.
	(GRUB_AFFS_FILETYPE_DIR), (GRUB_AFFS_FILETYPE_REG): Fix a mix-up.
	(grub_fshelp_node): Make block 32-bit.
	Add block_cache and last_block_cache.
	(grub_affs_read_block): Fill and use block cache.
	(grub_affs_read_file): Removed.
	(grub_affs_mount): Zero-fill node. Fix version check. Don't reread
	boot block.
	(grub_affs_read_symlink): Fix symlink size. Add a \0 at the end for
	safety.
	(grub_affs_iterate_dir): Use more appropriate types. Zero-fill allocated
	space.
	(grub_affs_close): Free block cache.
	(grub_affs_read): Use grub_fshelp_read_file directly.