### 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.

{
    assert(pindexNew->pprev == chainActive.Tip());
    
    int64_t nTime1 = GetTimeMicros();
    if (!pblock) {
        std::shared_ptr<CBlock> pblockNew = std::make_shared<CBlock>();
        connectTrace.blocksConnected.emplace_back(pindexNew, pblockNew);
        if (!ReadBlockFromDisk(*pblockNew, pindexNew, chainparams.GetConsensus()))
            return AbortNode(state, "Failed to read block");
    } else {
        connectTrace.blocksConnected.emplace_back(pindexNew, pblock);
    }
    const CBlock& blockConnecting = *connectTrace.blocksConnected.back().second;
    
    int64_t nTime2 = GetTimeMicros(); nTimeReadFromDisk += nTime2 - nTime1;
    int64_t nTime3;
    LogPrint("bench", "  - Load block from disk: %.2fms [%.2fs]\n", (nTime2 - nTime1) * 0.001, nTimeReadFromDisk * 0.000001);
    {
        CCoinsViewCache view(pcoinsTip);
        bool rv = ConnectBlock(blockConnecting, state, pindexNew, view, chainparams);
        GetMainSignals().BlockChecked(blockConnecting, state);
        if (!rv) {