Check whether a particular flag is set in a flags field.
@param field_name the name of the flag field option
@param flag_name the name of the flag to check
@return non-zero if the flag is set, zero if the flag isn't set,
isn't of the right type, or the flags field doesn't exist.
Check whether a particular flag is set in a flags field.
@param field_name the name of the flag field option @param flag_name the name of the flag to check @return non-zero if the flag is set, zero if the flag isn't set, isn't of the right type, or the flags field doesn't exist.