### 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.

}
/**
 * Calculates the block height and previous block's median time past at
 * which the transaction will be considered final in the context of BIP 68.
 * Also removes from the vector of input heights any entries which did not
 * correspond to sequence locked inputs as they do not affect the calculation.
 */
static std::pair<int, int64_t> CalculateSequenceLocks(const CTransaction &tx, int flags, std::vector<int>* prevHeights, const CBlockIndex& block)
{
    assert(prevHeights->size() == tx.vin.size());
    
    
    
    
    
    int nMinHeight = -1;
    int64_t nMinTime = -1;
    
    
    
    bool fEnforceBIP68 = static_cast<uint32_t>(tx.nVersion) >= 2
                      && flags & LOCKTIME_VERIFY_SEQUENCE;
    
    
    if (!fEnforceBIP68) {
        return std::make_pair(nMinHeight, nMinTime);
    }
    for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
        const CTxIn& txin = tx.vin[txinIndex];