Default to ActiveSupport::Notifications for pg and mysql2 (#583)

background: #418

By default, rack mini profiler is expected to use active support notifications

Before
======

Oracle is working as described, but pg and mysql are not.

SqlPatches.sql_patches returns ["pg"] for postgres, patches postgres,
and does not leverage ActiveSupport::Notifications

After
=====

Like oracle, postgres and mysql are double checking with patch_rails? to determine if the
rails code should be patched.

SqlPatches.sql_patches returns [] for postgres

lib/patches/sql_patches.rb

@@ -30,8 +30,8 @@ def self.patch_rails?
   def self.sql_patches
     patches = []
 
-    patches << 'mysql2' if defined?(Mysql2::Client) && Mysql2::Client.class == Class
-    patches << 'pg' if defined?(PG::Result) && PG::Result.class == Class
+    patches << 'mysql2' if defined?(Mysql2::Client) && Mysql2::Client.class == Class && patch_rails?
+    patches << 'pg' if defined?(PG::Result) && PG::Result.class == Class && patch_rails?
     patches << 'oracle_enhanced' if defined?(ActiveRecord::ConnectionAdapters::OracleEnhancedAdapter) && ActiveRecord::ConnectionAdapters::OracleEnhancedAdapter.class == Class &&
                                     SqlPatches.correct_version?('~> 1.5.0', ActiveRecord::ConnectionAdapters::OracleEnhancedAdapter) &&
                                     patch_rails?