### 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.

{
    const int nHeight = pindexPrev == NULL ? 0 : pindexPrev->nHeight + 1;
    
    if (block.nBits != GetNextWorkRequired(pindexPrev, &block, consensusParams))
        return state.DoS(100, false, REJECT_INVALID, "bad-diffbits", false, "incorrect proof of work");
    
    if (block.GetBlockTime() <= pindexPrev->GetMedianTimePast())
        return state.Invalid(false, REJECT_INVALID, "time-too-old", "block's timestamp is too early");
    
    if (block.GetBlockTime() > nAdjustedTime + 2 * 60 * 60)
        return state.Invalid(false, REJECT_INVALID, "time-too-new", "block timestamp too far in the future");
    
    
    if((block.nVersion < 2 && nHeight >= consensusParams.BIP34Height) ||
       (block.nVersion < 3 && nHeight >= consensusParams.BIP66Height) ||
       (block.nVersion < 4 && nHeight >= consensusParams.BIP65Height))
            return state.Invalid(false, REJECT_OBSOLETE, strprintf("bad-version(0x%08x)", block.nVersion),
                                 strprintf("rejected nVersion=0x%08x block", block.nVersion));
    return true;
}
bool ContextualCheckBlock(const CBlock& block, CValidationState& state, const Consensus::Params& consensusParams, const CBlockIndex* pindexPrev)