I believe column access via `__getattr__` is bad and shouldn't be implicitly encouraged by the error message when accessing a non-existing attribute on DataFrame. This patch changes the error message from 'no such column'  to the more generic 'no such attribute', which is also what Pandas DFs will throw.

Author: ksonj <kson@siberie.de>

Closes #5771 from ksonj/master and squashes the following commits:

bcc2220 [ksonj] Better error message on access to non-existing attribute