variable in where clause.

Problem: the new_item() method of Item_uint used an incorrect
constructor. "new Item_uint(name, max_length)" calls
Item_uint::Item_uint(const char *str_arg, uint length) which assumes the
first argument to be the string representation of the value, not the
item's name. This could result in either a server crash or incorrect
results depending on usage scenarios.

Fixed by using the correct constructor in new_item():
Item_uint::Item_uint(const char *str_arg, longlong i, uint length).