character set introducer": add new item type to be returned before from 
Item_param until it's value is set.
This way items like Item_bool_func2 and udf_handler won't treat this item
as constant literal when statement is prepared.


mysql-test/r/ps.result:
  Test results fixed (test case for bug #4105)
mysql-test/t/ps.test:
  Followup to bug #4105: a test case.
sql/item.cc:
  Fix for bug#4105 "Server crash on attempt to prepare a statement with 
  character set introducer": add new item type to be returned before from 
  Item_param until it's value is set.
sql/item.h:
  Fix for bug#4105 "Server crash on attempt to prepare a statement with 
  character set introducer": add new item type to be returned before from 
  Item_param until it's value is set.