tor/changes/bug17852

  o Minor features (code hardening):
    - Use tor_snprintf() and tor_vsnprintf() even in external and
      low-level code, to harden against accidental failures to NUL-
      terminate. Part of ticket 17852. Patch from 'jsturgix'. Found
      with Flawfinder.

  o Minor bugfixes (private directory):
    - Prevent a race condition when creating private directories.
      Fixes part of bug 17852; bugfix on 0.2pre13. Part of ticket
      17852. Patch from 'jsturgix'. Found with Flawfinder.