### 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.

if (pa->nChainWork > pb->nChainWork) return false;
            if (pa->nChainWork < pb->nChainWork) return true;
            
            if (pa->nSequenceId < pb->nSequenceId) return false;
            if (pa->nSequenceId > pb->nSequenceId) return true;
            
            
            if (pa < pb) return false;
            if (pa > pb) return true;
            
            return false;
        }
    };
    CBlockIndex *pindexBestInvalid;
    /**
     * The set of all CBlockIndex entries with BLOCK_VALID_TRANSACTIONS (for itself and all ancestors) and
     * as good as our current tip or better. Entries may be failed, though, and pruning nodes may be
     * missing the data for the block.
     */
    std::set<CBlockIndex*, CBlockIndexWorkComparator> setBlockIndexCandidates;
    /** All pairs A->B, where A (or one of its ancestors) misses transactions, but B has transactions.
     * Pruned nodes may have entries where B is missing data.
     */
    std::multimap<CBlockIndex*, CBlockIndex*> mapBlocksUnlinked;
    CCriticalSection cs_LastBlockFile;
    std::vector<CBlockFileInfo> vinfoBlockFile;