The patch implements cleanup of device path on devfs_remove. It does not
use extra counters as was suggested once - rather it simply removes all
empty directories. Manually created directories (and connecting paths)
are preserved and cleaned up on rmdir/unlink.

The creation/removing of path is not atomic; it will be addressed later.
It apparently requires replacing per-directory locks with global one;
using extra counters does not actually helps here.

This patch will cause devfs_remove on directories emit warning in most
cases. Removing connecting directories makes no sense with this change
so if it is agreed upon I send patch that removes all
devfs_remove("directory") from kernel. It was never done consistently
anyway. I would actually make
devfs_mk_dir noop except for two places - /dev/pts and /dev/shm.

regards

-andrey