remove using namespace std from merkleblock.cpp
remove using namespace std from merkleblock.cpp

bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic,zander/bitcoinclassic,bitcoinclassic/bitcoinclassic,bitcoinclassic/bitcoinclassic,bitcoinclassic/bitcoinclassic,zander/bitcoinclassic