Make this work with Linux 2.2 kernels again. In particular,

Make this work with Linux 2.2 kernels again.  In particular,

- Use the DCOUNT() macro from afs.h instead of atomic_read, because
  the d_count member of a struct dentry is an int in the 2.2 series,
  not an atomic_t.

- Use list_del() + INIT_LIST_HEAD() on 2.2, which doesn't have list_del_init().

- BUG() only exists on 2.4 kernels.  Just don't use it on 2.2.

(cherry picked from commit f8d781408717fbf65837fc69d4b4edda2349df4f)