### 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 (fHavePruned)
        LogPrintf("LoadBlockIndexDB(): Block files have previously been pruned\n");
    
    bool fReindexing = false;
    pblocktree->ReadReindexing(fReindexing);
    fReindex |= fReindexing;
    
    pblocktree->ReadFlag("txindex", fTxIndex);
    LogPrintf("%s: transaction index %s\n", __func__, fTxIndex ? "enabled" : "disabled");
    
    BlockMap::iterator it = mapBlockIndex.find(pcoinsTip->GetBestBlock());
    if (it == mapBlockIndex.end())
        return true;
    chainActive.SetTip(it->second);
    PruneBlockIndexCandidates();
    LogPrintf("%s: hashBestChain=%s height=%d date=%s progress=%f\n", __func__,
        chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(),
        DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),
        GuessVerificationProgress(chainparams.TxData(), chainActive.Tip()));
    return true;
}
CVerifyDB::CVerifyDB()
{
    uiInterface.ShowProgress(_("Verifying blocks..."), 0);
}
CVerifyDB::~CVerifyDB()
{
    uiInterface.ShowProgress("", 100);
}
bool CVerifyDB::VerifyDB(const CChainParams& chainparams, CCoinsView *coinsview, int nCheckLevel, int nCheckDepth)