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/hostfs/hostfs_kern.c

@@ -738,6 +738,9 @@ int hostfs_rename(struct inode *from_ino, struct dentry *from,
 	char *from_name, *to_name;
 	int err;
 
+	if (to->d_inode && S_ISDIR(to->d_inode->i_mode))
+		dentry_unhash(to);
+
 	if ((from_name = dentry_name(from)) == NULL)
 		return -ENOMEM;
 	if ((to_name = dentry_name(to)) == NULL) {