tor/changes/stack

  o Minor bugfixes (correctness):
    - Fix several places in our codebase where a C compiler would be likely
      to eliminate a check, based on assuming that undefined behavior had not
      happened elsewhere in the code.  These cases are usually a sign of
      redundant checking, or dubious arithmetic. Found by Georg Koppen using
      the "STACK" tool from Wang, Zeldovich, Kaashoek, and
      Solar-Lezama. Fixes bug 24423; bugfix on various Tor versions.