message: [RPC] Add mediantime to getblock/getblockheader output
  Simple addition to the JSON output; mainly used in upcoming functional
  test updates.
diff: @@ -66,6 +66,7 @@ UniValue blockheaderToJSON(const CBlockIndex* blockindex)
  result.push_back(Pair("version", blockindex->nVersion));
  result.push_back(Pair("merkleroot", blockindex->hashMerkleRoot.GetHex()));
  result.push_back(Pair("time", (int64_t)blockindex->nTime));
  + result.push_back(Pair("mediantime", (int64_t)blockindex->GetMedianTimePast()));
  result.push_back(Pair("nonce", (uint64_t)blockindex->nNonce));
  result.push_back(Pair("bits", strprintf("%08x", blockindex->nBits)));
  result.push_back(Pair("difficulty", GetDifficulty(blockindex)));
  @@ -105,6 +106,7 @@ UniValue blockToJSON(const CBlock& block, const CBlockIndex* blockindex, bool tx
  }
  result.push_back(Pair("tx", txs));
  result.push_back(Pair("time", block.GetBlockTime()));
  + result.push_back(Pair("mediantime", (int64_t)blockindex->GetMedianTimePast()));
  result.push_back(Pair("nonce", (uint64_t)block.nNonce));
  result.push_back(Pair("bits", strprintf("%08x", block.nBits)));
  result.push_back(Pair("difficulty", GetDifficulty(blockindex)));
  @@ -317,6 +319,7 @@ UniValue getblock(const UniValue& params, bool fHelp)
  " ,...\n"
  " ],\n"
  " \"time\" : ttt, (numeric) The block time in seconds since epoch (Jan 1 1970 GMT)\n"
  + " \"mediantime\" : ttt, (numeric) The median block time in seconds since epoch (Jan 1 1970 GMT)\n"
  " \"nonce\" : n, (numeric) The nonce\n"
  " \"bits\" : \"1d00ffff\", (string) The bits\n"
  " \"difficulty\" : x.xxx, (numeric) The difficulty\n"
  @@ -390,8 +393,9 @@ UniValue getblockheader(const UniValue& params, bool fHelp)
  " \"previousblockhash\" : \"hash\", (string) The hash of the previous block\n"
  " \"merkleroot\" : \"xxxx\", (string) The merkle root\n"
  " \"time\" : ttt, (numeric) The block time in seconds since epoch (Jan 1 1970 GMT)\n"
  - " \"bits\" : \"1d00ffff\", (string) The bits\n"
  + " \"mediantime\" : ttt, (numeric) The median block time in seconds since epoch (Jan 1 1970 GMT)\n"
  " \"nonce\" : n, (numeric) The nonce\n"
  + " \"bits\" : \"1d00ffff\", (string) The bits\n"
  "}\n"
  "\nResult (for verbose=false):\n"
  