The right way to fix this is to change the Field::store(longlong) method to be
Field::store(longlong, bool unsigned_flag), but this is better to do in 4.1 than in 4.0


mysql-test/r/bigint.result:
  New tests to show how the last bigint patch broke MySQL
mysql-test/t/bigint.test:
  New tests to show how the last bigint patch broke MySQL
sql/item.cc:
  Revert patch for bigint handling in double context as it broke normal bigint handling
sql/item.h:
  Revert patch for bigint handling in double context as it broke normal bigint handling