message: Wipe zerocoin DB on reindex.
  The zerocoin database should be wiped on reindex. If leftover information from a fork is left in the db it can lead to potential validation issues in the future and isolated forks.
diff: @@ -1311,8 +1311,10 @@ bool AppInit2(boost::thread_group& threadGroup)
  delete zerocoinDB;
  delete pSporkDB;
  - zerocoinDB = new CZerocoinDB(0, false, false);
  + //PIVX specific: zerocoin and spork DB's
  + zerocoinDB = new CZerocoinDB(0, false, fReindex);
  pSporkDB = new CSporkDB(0, false, false);
  +
  pblocktree = new CBlockTreeDB(nBlockTreeDBCache, false, fReindex);
  pcoinsdbview = new CCoinsViewDB(nCoinDBCache, false, fReindex);
  pcoinscatcher = new CCoinsViewErrorCatcher(pcoinsdbview);
  