### 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.

}
    }
    int64_t nNow = GetTimeMicros();
    
    if (nLastWrite == 0) {
        nLastWrite = nNow;
    }
    if (nLastFlush == 0) {
        nLastFlush = nNow;
    }
    if (nLastSetChain == 0) {
        nLastSetChain = nNow;
    }
    int64_t nMempoolSizeMax = GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000;
    int64_t cacheSize = pcoinsTip->DynamicMemoryUsage();
    int64_t nTotalSpace = nCoinCacheUsage + std::max<int64_t>(nMempoolSizeMax - nMempoolUsage, 0);
    
    bool fCacheLarge = mode == FLUSH_STATE_PERIODIC && cacheSize > std::max((9 * nTotalSpace) / 10, nTotalSpace - 100 * 1024 * 1024);
    
    bool fCacheCritical = mode == FLUSH_STATE_IF_NEEDED && cacheSize > nTotalSpace;
    
    bool fPeriodicWrite = mode == FLUSH_STATE_PERIODIC && nNow > nLastWrite + (int64_t)DATABASE_WRITE_INTERVAL * 1000000;
    
    bool fPeriodicFlush = mode == FLUSH_STATE_PERIODIC && nNow > nLastFlush + (int64_t)DATABASE_FLUSH_INTERVAL * 1000000;
    
    bool fDoFullFlush = (mode == FLUSH_STATE_ALWAYS) || fCacheLarge || fCacheCritical || fPeriodicFlush || fFlushForPrune;
    
    if (fDoFullFlush || fPeriodicWrite) {
        
        if (!CheckDiskSpace(0))