### 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.

bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                        bool fOverrideMempoolLimit, const CAmount nAbsurdFee)
{
    std::vector<uint256> vHashTxToUncache;
    bool res = AcceptToMemoryPoolWorker(pool, state, tx, fLimitFree, pfMissingInputs, nAcceptTime, plTxnReplaced, fOverrideMempoolLimit, nAbsurdFee, vHashTxToUncache);
    if (!res) {
        BOOST_FOREACH(const uint256& hashTx, vHashTxToUncache)
            pcoinsTip->Uncache(hashTx);
    }
    
    CValidationState stateDummy;
    FlushStateToDisk(stateDummy, FLUSH_STATE_PERIODIC);
    return res;
}
bool AcceptToMemoryPool(CTxMemPool& pool, CValidationState &state, const CTransactionRef &tx, bool fLimitFree,
                        bool* pfMissingInputs, std::list<CTransactionRef>* plTxnReplaced,
                        bool fOverrideMempoolLimit, const CAmount nAbsurdFee)
{
    return AcceptToMemoryPoolWithTime(pool, state, tx, fLimitFree, pfMissingInputs, GetTime(), plTxnReplaced, fOverrideMempoolLimit, nAbsurdFee);
}
bool GetTransaction(const uint256 &hash, CTransactionRef &txOut, const Consensus::Params& consensusParams, uint256 &hashBlock, bool fAllowSlow)