* Remove the SINGLEUSE feature for telldir(), it does not conform to the
Open Group specification.
* Add a mutex around the ddloc hash table. Note that NetBSD implemented
a per-dirp list but telldir/seekdir performance just isn't an issue
for these functions so stick with the global hash table.
* Reuse the ddloc for a previous seekdir() when calling telldir() just
after a seekdir(), instead of allocating a new one.
* rewinddir() now cleans up any ddloc's for the dirp.
Reported-by: Gary Stanley <sinknull@crater.dragonflybsd.org>