### 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.

{
    {
        CBlockIndex *pindex = NULL;
        if (fNewBlock) *fNewBlock = false;
        CValidationState state;
        
        
        bool ret = CheckBlock(*pblock, state, chainparams.GetConsensus());
        LOCK(cs_main);
        if (ret) {
            
            ret = AcceptBlock(pblock, state, chainparams, &pindex, fForceProcessing, NULL, fNewBlock);
        }
        CheckBlockIndex(chainparams.GetConsensus());
        if (!ret) {
            GetMainSignals().BlockChecked(*pblock, state);
            return error("%s: AcceptBlock FAILED", __func__);
        }
    }
    NotifyHeaderTip();
    CValidationState state; 
    if (!ActivateBestChain(state, chainparams, pblock))
        return error("%s: ActivateBestChain failed", __func__);
    return true;
}
bool TestBlockValidity(CValidationState& state, const CChainParams& chainparams, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW, bool fCheckMerkleRoot)