### 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.

mempool.PrioritiseTransaction(tx->GetHash(), tx->GetHash().ToString(), prioritydummy, amountdelta);
            }
            CValidationState state;
            if (nTime + nExpiryTimeout > nNow) {
                LOCK(cs_main);
                AcceptToMemoryPoolWithTime(mempool, state, tx, true, NULL, nTime);
                if (state.IsValid()) {
                    ++count;
                } else {
                    ++failed;
                }
            } else {
                ++skipped;
            }
            if (ShutdownRequested())
                return false;
        }
        std::map<uint256, CAmount> mapDeltas;
        file >> mapDeltas;
        for (const auto& i : mapDeltas) {
            mempool.PrioritiseTransaction(i.first, i.first.ToString(), prioritydummy, i.second);
        }
    } catch (const std::exception& e) {
        LogPrintf("Failed to deserialize mempool data on disk: %s. Continuing anyway.\n", e.what());
        return false;
    }
    LogPrintf("Imported mempool transactions from disk: %i successes, %i failed, %i expired\n", count, failed, skipped);
    return true;
}
void DumpMempool(void)