Checkpoints::GetTotalBlocksEstimate will probably fail/produce wrong results

[nvmd]

Checkpoints::GetTotalBlocksEstimate will probably fail/produce wrong results on 0.10 branch (commit 047a89831760ff124740fe9f58411d57ee087078).

• No checkpoints - SIGSEGV accessing empty MapCheckpoints (i.e. std::map).
• N > 1 checkpoint - result is less than expected (by 1), but this probably doesn't make much sense
• Genesis block only - 0, but should be 1 - can probably break something

checkpoints.cpp:72-80

    int GetTotalBlocksEstimate()
    {
        if (!fEnabled)
            return 0;

        const MapCheckpoints& checkpoints = *Params().Checkpoints().mapCheckpoints;

        return checkpoints.rbegin()->first;
    }

Suggest to change checkpoints.cpp:79 from return checkpoints.rbegin()->first; to return checkpoints.rbegin()->first + 1;