Avoid getting redefined method warning

Warning:

  ~/projects/rails/activerecord/lib/active_record/railtie.rb:140: warning: method redefined; discarding old extend_message
  ~/projects/rails/activerecord/lib/active_record/errors.rb:104: warning: previous definition of extend_message was here
Cast env to symbol, fixes deprecation warning

Warning:

  DEPRECATION WARNING: Passing a string to ActiveRecord::Base.establish_connection for a configuration lookup is deprecated, please pass a symbol (:development) instead.