### 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.

if (pindex->nHeight >= chainparams.GetConsensus().BIP65Height) {
        flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
    }
    
    int nLockTimeFlags = 0;
    if (VersionBitsState(pindex->pprev, chainparams.GetConsensus(), Consensus::DEPLOYMENT_CSV, versionbitscache) == THRESHOLD_ACTIVE) {
        flags |= SCRIPT_VERIFY_CHECKSEQUENCEVERIFY;
        nLockTimeFlags |= LOCKTIME_VERIFY_SEQUENCE;
    }
    
    if (IsWitnessEnabled(pindex->pprev, chainparams.GetConsensus())) {
        flags |= SCRIPT_VERIFY_WITNESS;
        flags |= SCRIPT_VERIFY_NULLDUMMY;
    }
    int64_t nTime2 = GetTimeMicros(); nTimeForks += nTime2 - nTime1;
    LogPrint("bench", "    - Fork checks: %.2fms [%.2fs]\n", 0.001 * (nTime2 - nTime1), nTimeForks * 0.000001);
    CBlockUndo blockundo;
    CCheckQueueControl<CScriptCheck> control(fScriptChecks && nScriptCheckThreads ? &scriptcheckqueue : NULL);
    std::vector<int> prevheights;
    CAmount nFees = 0;
    int nInputs = 0;
    int64_t nSigOpsCost = 0;
    CDiskTxPos pos(pindex->GetBlockPos(), GetSizeOfCompactSize(block.vtx.size()));
    std::vector<std::pair<uint256, CDiskTxPos> > vPos;
    vPos.reserve(block.vtx.size());
    blockundo.vtxundo.reserve(block.vtx.size() - 1);
    std::vector<PrecomputedTransactionData> txdata;
    txdata.reserve(block.vtx.size()); 
    for (unsigned int i = 0; i < block.vtx.size(); i++)
    {