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>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c692dad..3a33ae3 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6994,6 +6994,9 @@
 	u64 root_objectid;
 	int ret;
 
+	if (new_inode && S_ISDIR(new_dentry->d_inode->i_mode))
+		dentry_unhash(new_dentry);
+
 	if (new_dir->i_ino == BTRFS_EMPTY_SUBVOL_DIR_OBJECTID)
 		return -EPERM;