### 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 (outsBlock.nVersion < 0)
            outs->nVersion = outsBlock.nVersion;
        if (*outs != outsBlock)
            fClean = fClean && error("DisconnectBlock(): added transaction mismatch? database corrupted");
        
        outs->Clear();
        }
        
        if (i > 0) { 
            const CTxUndo &txundo = blockUndo.vtxundo[i-1];
            if (txundo.vprevout.size() != tx.vin.size())
                return error("DisconnectBlock(): transaction and undo data inconsistent");
            for (unsigned int j = tx.vin.size(); j-- > 0;) {
                const COutPoint &out = tx.vin[j].prevout;
                const CTxInUndo &undo = txundo.vprevout[j];
                if (!ApplyTxInUndo(undo, view, out))
                    fClean = false;
            }
        }
    }
    
    view.SetBestBlock(pindex->pprev->GetBlockHash());
    if (pfClean) {
        *pfClean = fClean;
        return true;
    }
    return fClean;
}
void static FlushBlockFile(bool fFinalize = false)