Reported here: https://github.com/bitcoin/bitcoin/pull/10244#issuecomment-378035305

Travis log here: https://travis-ci.org/bitcoin/bitcoin/jobs/361243719#L2810

Note the JSON exception:

```
test_framework.authproxy.JSONRPCException: The mempool was not loaded yet (-1) 
```

That exception was introduced here: https://github.com/bitcoin/bitcoin/commit/cb1e319fe9e198c9c5cf5236fe9af5a3d748b9e8#diff-a0c8f511d90e83aa9b5857e819ced344R1617

cc @jtimon 
{
        /* Make sure that unequal blocks with the same height do not compare
           equal. Use the pointers themselves to make a distinction. */
        if (a->nHeight != b->nHeight)
          return (a->nHeight > b->nHeight);
        return a < b;
    }
};
static UniValue getchaintips(const JSONRPCRequest& request)
{
    if (request.fHelp || request.params.size() != 0)
        throw std::runtime_error(
            RPCHelpMan{"getchaintips",
                "Return information about all known tips in the block tree,"
                " including the main chain as well as orphaned branches.\n",
                {},
                RPCResult{
            "[\n"
            "  {\n"
            "    \"height\": xxxx,         (numeric) height of the chain tip\n"
            "    \"hash\": \"xxxx\",         (string) block hash of the tip\n"
            "    \"branchlen\": 0          (numeric) zero for main chain\n"
            "    \"status\": \"active\"      (string) \"active\" for the main chain\n"
            "  },\n"
            "  {\n"
            "    \"height\": xxxx,\n"
            "    \"hash\": \"xxxx\",\n"