POSIX says that passing a location returned by telldir() to seekdir()

after an intervening call to rewinddir() is undefined, so reclaim any
pending telldir() cookies in the directory when rewinddir() is called.

CR:		D459
Reviewed by:	jilles
MFC after:	1 week

lib/libc/gen/rewinddir.c

@@ -58,6 +58,7 @@ rewinddir(dirp)
 		dirp->dd_seek = 0;
 	}
 	dirp->dd_loc = 0;
+	_reclaim_telldir(dirp);
 	if (__isthreaded)
 		_pthread_mutex_unlock(&dirp->dd_lock);
 }