The mismatch occurs on the function calls as in the sql/sql_udf.h the
types of "error" and "is_null" are unsigned char rather than char.
This is corrected for the udf functions:
* spider_direct_sql
* spider_direct_bg_sql
* spider_flush_table_mon_cache
* spider_copy_tables
* spider_ping_table
Reviewer: Yuchen Pei