the `zapwallettxes.py` qa test is currently broken due to a syntax error:

```python
     assert_raises(JSONRPCException, self.nodes[0].gettransaction, [txid3])
     #there must be a expection because the unconfirmed wallettx0 must be gone by now
```

This doesn't actually test that the transaction is not in the wallet, because `gettransaction()` is being called incorrectly (with an array instead of a string).

Changing the test to `assert_raises(JSONRPCException, self.nodes[0].gettransaction, txid3)` causes the rpc to succeed and the test script to fail because `txid3` is still in the wallet.

This is because the mempool is now persistent and is saved to disk when bitcoind shuts down. zapwallettxes removes the unconfirmed transaction from the wallet but bitcoind will rescan the mempool.dat file on startup and add the unconfirmed transaction back into the wallet.

I've 'fixed' zapwallettxes.py in https://github.com/jnewbery/bitcoin/tree/zapwallettxes , but the question remains: how *should* -zapwallettxes interact with persistent mempool? The use case for zapwallettxes is explained here: https://github.com/bitcoin/bitcoin/pull/3659#issuecomment-34878999 . My view is that even with zapwallettxes, bitcoind should rescan the mempool, but there should be better documentation or a warning that unconfirmed transaction in your mempool will be re-added to the wallet even if zapwallettxes is used. If you really want to remove all unconfirmed transactions from your wallet, you can delete your mempool.dat file and then restart with zapwallettxes.
void PruneBlockFilesManual(int nPruneUpToHeight);
/** (try to) add transaction to memory pool
 * plTxnReplaced will be appended to with all transactions replaced from mempool **/
bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx, bool fLimitFree,
                        bool* pfMissingInputs, std::list<CTransactionRef>* plTxnReplaced = NULL,
                        bool fOverrideMempoolLimit=false, const CAmount nAbsurdFee=0);
bool AcceptToMemoryPoolWithTime(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx, bool fLimitFree,
                        bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced = NULL,
                        bool fOverrideMempoolLimit=false, const CAmount nAbsurdFee=0);
std::string FormatStateMessage(const CValidationState &state);
ThresholdState VersionBitsTipState(const Consensus::Params& params, Consensus::DeploymentPos pos);
int VersionBitsTipStateSinceHeight(const Consensus::Params& params, Consensus::DeploymentPos pos);
/** 
 * Count ECDSA signature operations the old-fashioned (pre-0.6) way
 * @return number of sigops this transaction's outputs will produce when spent
 * @see CTransaction::FetchInputs
 */
unsigned int GetLegacySigOpCount(const CTransaction& tx);
/**
 * Count ECDSA signature operations in pay-to-script-hash inputs.
 * 
 * @param[in] mapInputs Map of previous transactions that have outputs we're spending
 * @return maximum number of sigops required to validate this transaction's inputs
 * @see CTransaction::FetchInputs
 */
unsigned int GetP2SHSigOpCount(const CTransaction& tx, const CCoinsViewCache& mapInputs);
/**
 * Compute total signature operation cost of a transaction.
 * @param[in] tx     Transaction for which we are computing the cost
 * @param[in] inputs Map of previous transactions that have outputs we're spending