Support for foreign keys in create table

If foreign keys specified in create table, generated SQL is slightly more
efficient.

Definition:

    ```
    create_table :testings do |t|
      t.references :testing_parent, foreign_key: true
    end
    ```

Before:

    ```
    CREATE TABLE "testings" ("id" serial primary key, "testing_parent_id" integer);
    ALTER TABLE "testings" ADD CONSTRAINT "fk_rails_a196c353b2" FOREIGN KEY ("testing_parent_id") REFERENCES "testing_parents" ("id");
    ```

After:

    ```
    CREATE TABLE "testings" ("id" serial primary key, "testing_parent_id" integer, CONSTRAINT "fk_rails_a196c353b2" FOREIGN KEY ("testing_parent_id") REFERENCES "testing_parents" ("id"));
    ```

1 files changed, 8 insertions, 0 deletions

diff --git a/activerecord/test/cases/migration/references_foreign_key_test.rb b/activerecord/test/cases/migration/references_foreign_key_test.rb
index 1594f99852..4f0da999d8 100644
--- a/activerecord/test/cases/migration/references_foreign_key_test.rb
+++ b/activerecord/test/cases/migration/references_foreign_key_test.rb
@@ -32,6 +32,14 @@ module ActiveRecord
         assert_equal [], @connection.foreign_keys("testings")
       end
 
+      test "foreign keys can be created in one query" do
+        assert_queries(1) do
+          @connection.create_table :testings do |t|
+            t.references :testing_parent, foreign_key: true
+          end
+        end
+      end
+
       test "options hash can be passed" do
         @connection.change_table :testing_parents do |t|
           t.integer :other_id