Correctly dump native timestamp types for MySQL

The native timestamp type in MySQL is different from datetime type.
Internal representation of the timestamp type is UNIX time, This means
that timestamp columns are affected by time zone.

```
> SET time_zone = '+00:00';
Query OK, 0 rows affected (0.00 sec)

> INSERT INTO time_with_zone(ts,dt) VALUES (NOW(),NOW());
Query OK, 1 row affected (0.02 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 22:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)

> SET time_zone = '-08:00';
Query OK, 0 rows affected (0.00 sec)

> SELECT * FROM time_with_zone;
+---------------------+---------------------+
| ts                  | dt                  |
+---------------------+---------------------+
| 2016-02-07 14:11:44 | 2016-02-07 22:11:44 |
+---------------------+---------------------+
1 row in set (0.00 sec)
```

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 03c8644229..12386635f6 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -291,6 +291,14 @@ class PrimaryKeyAnyTypeTest < ActiveRecord::TestCase
     schema = dump_table_schema "barcodes"
     assert_match %r{create_table "barcodes", primary_key: "code", id: :string, limit: 42}, schema
   end
+
+  if current_adapter?(:Mysql2Adapter) && subsecond_precision_supported?
+    test "schema typed primary key column" do
+      @connection.create_table(:scheduled_logs, id: :timestamp, precision: 6, force: true)
+      schema = dump_table_schema("scheduled_logs")
+      assert_match %r/create_table "scheduled_logs", id: :timestamp, precision: 6/, schema
+    end
+  end
 end
 
 class CompositePrimaryKeyTest < ActiveRecord::TestCase