Teach PostgreSQLAdapter#reset! to actually reset

It wasn't doing anything beyond clearing the statement cache.

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -605,7 +605,12 @@ def reconnect!
 
       def reset!
         clear_cache!
-        super
+        reset_transaction
+        unless @connection.transaction_status == ::PG::PQTRANS_IDLE
+          @connection.query 'ROLLBACK'
+        end
+        @connection.query 'DISCARD ALL'
+        configure_connection
       end
 
       # Disconnects from the database if already connected. Otherwise, this

activerecord/test/cases/adapters/postgresql/connection_test.rb

@@ -45,6 +45,37 @@ def test_connection_options
       assert_equal 'off', expect
     end
 
+    def test_reset
+      @connection.query('ROLLBACK')
+      @connection.query('SET geqo TO off')
+
+      # Verify the setting has been applied.
+      expect = @connection.query('show geqo').first.first
+      assert_equal 'off', expect
+
+      @connection.reset!
+
+      # Verify the setting has been cleared.
+      expect = @connection.query('show geqo').first.first
+      assert_equal 'on', expect
+    end
+
+    def test_reset_with_transaction
+      @connection.query('ROLLBACK')
+      @connection.query('SET geqo TO off')
+
+      # Verify the setting has been applied.
+      expect = @connection.query('show geqo').first.first
+      assert_equal 'off', expect
+
+      @connection.query('BEGIN')
+      @connection.reset!
+
+      # Verify the setting has been cleared.
+      expect = @connection.query('show geqo').first.first
+      assert_equal 'on', expect
+    end
+
     def test_tables_logs_name
       @connection.tables('hello')
       assert_equal 'SCHEMA', @subscriber.logged[0][1]