- Stored procedures returning unsinged values returns signed values if
  text protocol is used. The reason is that the stored proceedure item
  Item_func_sp wasn't initializing the member variables properly based
  on the information contained in the associated result field.
- The patch is to upon field-item association, ::fix_fields, initialize
  the member variables in appropriate order.
- Field type of an Item_func_sp was hard coded to MYSQL_TYPE_VARCHAR.
  This is changed to return the type of the actual result field.
- Member function name sp_result_field was refactored to the more 
  appropriate init_result_field.
- Member function name find_and_check_access was refactored to 
  sp_check_access.