reiserfs: Clean up xattrs when REISERFS_FS_XATTR is unset

The current reiserfs xattr implementation will not clean up old xattr
files if files are deleted when REISERFS_FS_XATTR is unset.  This
results in inaccessible lost files, wasting space.

This patch compiles in basic xattr knowledge, such as how to delete them
and change ownership for quota tracking.  If the file system has never
used xattrs, then the operation is quite fast: it returns immediately
when it sees there is no .reiserfs_priv directory.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>