Clean-compile on 32-bit architectures

32-bit build errors like this:

    cpp-driver/src/connection.cpp: In member function ‘void cass::Connection::consume(char*, size_t)’:
    cpp-driver/src/connection.cpp:301: error: format ‘%lu’ expects type ‘long unsigned int’, but argument 7 has type ‘size_t’

I've fixed by casting to int, failing to find a more portable solution.