The addition of i_dirhash to struct inode pushed RELENG_4's

The addition of i_dirhash to struct inode pushed RELENG_4's
sizeof(struct inode) into a new malloc bucket on the i386. This
didn't happen in -current due to the removal of i_lock, but it does
no harm to apply the workaround to -current first.

Reduce the size of the i_spare[] array in struct inode from 4 to
3 entries, and change ext2fs to use i_din.di_spare[1] so that it
does not need i_spare[3].

Reviewed by:	bde
MFC after:	3 days