### 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.

{
    int64_t nSigOps = GetLegacySigOpCount(tx) * WITNESS_SCALE_FACTOR;
    if (tx.IsCoinBase())
        return nSigOps;
    if (flags & SCRIPT_VERIFY_P2SH) {
        nSigOps += GetP2SHSigOpCount(tx, inputs) * WITNESS_SCALE_FACTOR;
    }
    for (unsigned int i = 0; i < tx.vin.size(); i++)
    {
        const CTxOut &prevout = inputs.GetOutputFor(tx.vin[i]);
        nSigOps += CountWitnessSigOps(tx.vin[i].scriptSig, prevout.scriptPubKey, &tx.vin[i].scriptWitness, flags);
    }
    return nSigOps;
}
bool CheckTransaction(const CTransaction& tx, CValidationState &state, bool fCheckDuplicateInputs)
{
    
    if (tx.vin.empty())
        return state.DoS(10, false, REJECT_INVALID, "bad-txns-vin-empty");
    if (tx.vout.empty())
        return state.DoS(10, false, REJECT_INVALID, "bad-txns-vout-empty");
    
    if (::GetSerializeSize(tx, SER_NETWORK, PROTOCOL_VERSION | SERIALIZE_TRANSACTION_NO_WITNESS) > MAX_BLOCK_BASE_SIZE)
        return state.DoS(100, false, REJECT_INVALID, "bad-txns-oversize");
    
    CAmount nValueOut = 0;
    for (const auto& txout : tx.vout)
    {
        if (txout.nValue < 0)