MySQL: we can't distinguish a fake 0 default in 4.x

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@8272 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

activerecord/test/defaults_test.rb

@@ -31,7 +31,8 @@ def test_mysql_integer_not_null_defaults
 
       assert_equal 0, klass.columns_hash['zero'].default
       assert !klass.columns_hash['zero'].null
-      assert_equal nil, klass.columns_hash['omit'].default
+      # 0 in MySQL 4, nil in 5.
+      assert [0, nil].include?(klass.columns_hash['omit'].default)
       assert !klass.columns_hash['omit'].null
 
       assert_raise(ActiveRecord::StatementInvalid) { klass.create! }