crash when Query::parse process param more then 127

[H jj]

Hi:
     mysql++-3.1.0.tar.gz
     $ ./configure --with-field-limit=150

     code example
====
     mysqlpp::Query query = dbcon->query();
     query<<"call some_proc(%0:Qname, ......,%128:some)";
     query.parse();
====
     then crash at query.cpp:338  parsed_names_[n] = name;
     because n is signed char at query.cpp:296  signed char n = atoi(num);
     in example atoi(num) eq 128,   but n is signed char, so  n is -128