### Describe the issue

Restarting bitcoin, mempool starts filling from scratch.

### Can you reliably reproduce the issue?
#### If so, please list the steps to reproduce below:
1. Wait for mempool to reach for example 3000 transactions
2. Restart bitcoin
3. Watch mempool filling slowly from scratch

### Expected behaviour
Mempool would already contain ~3000 TX on startup

### Actual behaviour
It starts at 0 and fills up slowly with a few per second.

### Screenshots.
http://imgur.com/a/or82d

### What version of bitcoin-core are you using?
Windows x64 0.14rc1 binary from https://bitcoin.org/bin/bitcoin-core-0.14.0/test.rc1/


### Any extra information that might be useful in the debugging process.
I may not be aware of how the mempool.dat thing works and there could just be a misunderstanding.

bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                              bool fOverrideMempoolLimit, const CAmount& nAbsurdFee, std::vector<uint256>& vHashTxnToUncache)
{
    const CTransaction& tx = *ptx;
    const uint256 hash = tx.GetHash();
    AssertLockHeld(cs_main);
    if (pfMissingInputs)
        *pfMissingInputs = false;
    if (!CheckTransaction(tx, state))
        return false; 
    
    if (tx.IsCoinBase())
        return state.DoS(100, false, REJECT_INVALID, "coinbase");
    
    bool witnessEnabled = IsWitnessEnabled(chainActive.Tip(), Params().GetConsensus());
    if (!GetBoolArg("-prematurewitness",false) && tx.HasWitness() && !witnessEnabled) {
        return state.DoS(0, false, REJECT_NONSTANDARD, "no-witness-yet", true);
    }
    
    std::string reason;
    if (fRequireStandard && !IsStandardTx(tx, reason, witnessEnabled))
        return state.DoS(0, false, REJECT_NONSTANDARD, reason);
    
    
    
    if (!CheckFinalTx(tx, STANDARD_LOCKTIME_VERIFY_FLAGS))
        return state.DoS(0, false, REJECT_NONSTANDARD, "non-final");