Fix CI failure due to reference type mismatch

`Firm.id` is a bigint if mysql2 adapter is used, but `firm_id` is an
integer. It will cause an out of range error.

https://travis-ci.org/rails/rails/jobs/264112814#L776
https://travis-ci.org/rails/rails/jobs/264112835#L919

activerecord/test/cases/base_test.rb

@@ -885,10 +885,17 @@ def test_dup_of_saved_object_marks_as_dirty_only_changed_attributes
 
   def test_bignum
     company = Company.find(1)
-    company.rating = 2147483647
+    company.rating = 2147483648
     company.save
     company = Company.find(1)
-    assert_equal 2147483647, company.rating
+    assert_equal 2147483648, company.rating
+  end
+
+  unless current_adapter?(:SQLite3Adapter)
+    def test_bignum_pk
+      company = Company.create!(id: 2147483648, name: "foo")
+      assert_equal company, Company.find(company.id)
+    end
   end
 
   # TODO: extend defaults tests to other databases!

activerecord/test/schema/schema.rb

@@ -9,7 +9,7 @@
   # ------------------------------------------------------------------- #
 
   create_table :accounts, force: true do |t|
-    t.integer :firm_id
+    t.references :firm, index: false
     t.string  :firm_name
     t.integer :credit_limit
   end
@@ -197,11 +197,11 @@
 
   create_table :companies, force: true do |t|
     t.string  :type
-    t.integer :firm_id
+    t.references :firm, index: false
     t.string  :firm_name
     t.string  :name
-    t.integer :client_of
-    t.integer :rating, default: 1
+    t.bigint :client_of
+    t.bigint :rating, default: 1
     t.integer :account_id
     t.string :description, default: ""
     t.index [:firm_id, :type, :rating], name: "company_index", length: { type: 10 }, order: { rating: :desc }
@@ -236,8 +236,8 @@
   end
 
   create_table :contracts, force: true do |t|
-    t.integer :developer_id
-    t.integer :company_id
+    t.references :developer, index: false
+    t.references :company, index: false
   end
 
   create_table :customers, force: true do |t|
@@ -263,7 +263,7 @@
     t.string   :name
     t.string   :first_name
     t.integer  :salary, default: 70000
-    t.integer :firm_id
+    t.references :firm, index: false
     t.integer :mentor_id
     if subsecond_precision_supported?
       t.datetime :created_at, precision: 6
@@ -720,7 +720,7 @@
   create_table :projects, force: true do |t|
     t.string :name
     t.string :type
-    t.integer :firm_id
+    t.references :firm, index: false
     t.integer :mentor_id
   end
 
@@ -809,8 +809,7 @@
 
   create_table :sponsors, force: true do |t|
     t.integer :club_id
-    t.integer :sponsorable_id
-    t.string :sponsorable_type
+    t.references :sponsorable, polymorphic: true, index: false
   end
 
   create_table :string_key_objects, id: false, force: true do |t|