tmpfs - Correct some timestamp update issues

tmpfs - Correct some timestamp update issues

* write() was updating ACCESSED and MODIFIED when it should only
  be updating MODIFIED.

* unlink() (aka rm) was updating CHANGE, ACCESSED, and MODIFIED
  which would be visible if a file has multiple links.  It should
  only update the CHANGE time.

* rmdir() was doing the same thing as UNLINKED.  Fixed this too,
  but the bug would not be readily visible anyway since directories
  cannot be hardlinked.  However, fstat() on an open descriptor
  would still reveal it.