vfs: push dentry_unhash on rename_dir into file systems

Only a few file systems need this.  Start by pushing it down into each
rename method (except gfs2 and xfs) so that it can be dealt with on a
per-fs basis.

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nilfs2/namei.c

@@ -371,6 +371,9 @@ static int nilfs_rename(struct inode *old_dir, struct dentry *old_dentry,
 	struct nilfs_transaction_info ti;
 	int err;
 
+	if (new_inode && S_ISDIR(new_inode->i_mode))
+		dentry_unhash(new_dentry);
+
 	err = nilfs_transaction_begin(old_dir->i_sb, &ti, 1);
 	if (unlikely(err))
 		return err;