Fix multiple issues with -p<parallel>, including several data corruption

Fix multiple issues with -p<parallel>, including several data corruption
issues.

* Use malloc'd buffers instead of static buffers
* Fix memory leaks
* Fix races with hardlink tracking structures
* Fix bug in remote mknod (it wasn't creating the node on the remote host)
* Fix stack blowouts from deep recursions by starting a new thread.
* Postpend the pid for tmp file creation.