Propagation of a large unsigned numeric constant
in the WHERE expression led to wrong result.

For example,
"WHERE a = CAST(0xFFFFFFFFFFFFFFFF AS USIGNED) AND FOO(a)",
where a is an UNSIGNED BIGINT, and FOO() accepts strings,
was transformed to "... AND FOO('-1')".

That has been fixed.

Also EXPLAIN EXTENDED printed incorrect numeric constants in
transformed WHERE expressions like above. That has been
fixed too.


mysql-test/r/bigint.result:
  Added test case for bug #45360.
mysql-test/t/bigint.test:
  Added test case for bug #45360.
sql/item.cc:
  Bug #45360: wrong results
  
  As far as Item_int_with_ref (and underlaying Item_int)
  class accepts both signed and unsigned 64bit values,
  Item_int::val_str and Item_int::print methods have been
  modified to take into account unsigned_flag.