Custom Lookups & Transform example lhs/rhs swap

[Bruno Alla]

In the doc for lookups and transform, in the example on optimizing lookups:
​https://docs.djangoproject.com/en/1.9/howto/custom-lookups/#writing-an-efficient-abs-lt-lookup

The paragraph after the code snippets confused me:

There are a couple of notable things going on. First, AbsoluteValueLessThan isn’t calling process_lhs(). Instead it skips the transformation of the lhs done by AbsoluteValue and uses the original lhs. That is, we want to get 27 not ABS(27)

I initially though that lhs and rhs were swapped, but after asking on the #django IRC channel, I was advised that the confusion come from the last sentence, which should actually refer to the left of the SQL, rather than the right side:

That is, we want to get "experiments"."change" not ABS("experiments"."change")

Happy to submit a PR if suggested solution is accepted.

[Tim Graham]

​PR

[Tim Graham <timograham@…>]

In ffcdb0b:

Fixed #25893 -- Corrected custom lookups example.

[Tim Graham <timograham@…>]

In 740feb48:

[1.9.x] Fixed #25893 -- Corrected custom lookups example.

Backport of ffcdb0b471d0afc72b42b0a2b0c0c4fb45d7b6b1 from master

[Tim Graham <timograham@…>]

In c0c2c7e:

[1.8.x] Fixed #25893 -- Corrected custom lookups example.

Backport of ffcdb0b471d0afc72b42b0a2b0c0c4fb45d7b6b1 from master