"Negative integer keys incorrectly substituted for 0 during range analysis."

The problem is that the range optimizer incorrectly replaces any negative
constant with '0' for all types except BIGINT because the method save_in_field()
casts negative integers to non-negative. This causes incorrect query
results where (0 = any_negative_number).

The problem caused by this bug is fixed by the patch for BUG#11185.
That patch constitutes an optimization due to which the problem code is
never called with negative constants. This patch adds a test so we are sure
that the problem does not reappear.


mysql-test/r/select.result:
  Test for BUG#11521.
mysql-test/t/select.test:
  Test for BUG#11521.