Include query_scope in find_by methods

[shioyama]

It makes sense to include the query scope automatically in the find_by methods (find_by_title etc) so they work out of the box.

Assume title is a translated attribute:

Before

Post.i18n.find_by_title('foo')
#=> <Post ...>
Post.find_by_title('foo')
#=> ActiveRecord::StatementInvalid ...

After

Post.i18n.find_by_title('foo')
#=> <Post ...>
Post.find_by_title('foo')
#=> <Post ...>

[madhums]

Would be nice to merge this! @shioyama

[thisIsLoading]

yes, please, i just stumbled upon this in my new app. its unintuitive with the i18n