Connector/C++ ignores allowMultiQueries and injects savepoint names into SQL

Two independent defects in statement building. ConnectProtocol::createConnection passes the literal CLIENT_MULTI_STATEMENTS to mysql_real_connect and throws away the capability mask it just computed, so stacked statements are accepted on every connection even though allowMultiQueries defaults to …

    if (options->allowMultiQueries || (options->rewriteBatchedStatements)){
      capabilities|= MariaDbServerCapabilities::MULTI_STATEMENTS;
    }