Ugh.  nfs_unlink() is actually racy as hell - look what happens if
we enter it with ->d_count == 1, see that nfs_sillyrename() doesn't
need to do anything and call nfs_safe_remove().  In the meanwhile
somebody does dcache lookup (without going into NFS code - plain
and simple cache hit) and increments ->d_count.  nfs_safe_remove()
decides that something is very rotten and fails.

AFAICS we should take the test for ->d_count + d_drop if it's 1
under dcache_lock (and in one place).  Comments?

Proposed fix follows:
	* dget/dput killed in vfs_unlink() (safely)
	* nfs_unlink() starts with check for ->d_count (under dcache_lock)
	* if it's > 1 - sillyrename
	* if it is 1 - immediately unhash, then drop dcache_lock.
		after that we do as in old variant, except that
		rehashing is done in nfs_unlink() and only if there
		was an error - if there was none we simply leave
		d_delete() to vfs_unlink().