prepared statement

The method Item_func_in::build_clone() that builds a clone item for an
Item_func_in item first calls a generic method Item_func::build_item()
that builds the the clones for the arguments of the Item_func_in item
to be cloned, creates a copy of the Item_func_in object and attaches the
clones for the arguments to this copy. Then the method Item_func_in::build_clone()
makes the copy fully independent on the copied object in order to
guarantee a proper destruction of the clone. The fact is the copy of the
Item_func_in object is registered as any other item object and should be
destructed as any other item object.
If the method Item_func::build_item fails to build a clone of an argument
then it returns 0. In this case no copy of the Item_func_in object should
be created. Otherwise the finalizing actions for this copy would not be
performed and the copy would remain in a state that would prevent its
proper destruction.

The code of Item_func_in::build_clone() before this patch created the copy
of the Item_func_in object before cloning the argument items. If this
cloning failed the server crashed when trying to destruct the copy item.

The code of Item_row::build_clone() was changed similarly to the code of
Item_func::build_clone though this code could not cause any problems.