POST and DELETE operations in /users/me/alert_words may leave the
user's list of alert words in an unknown state: POSTing adds words to a
list that the client may not know from the begining, and the same with
DELETE.
Replying with the current status of the alert words list is the best way
of letting the client alter the list and knowing its contents after
being updated with a single query.
This is especially useful taking into account that POSTing words that
were already present and DELETing non-existing words both produce a
successful response.
An extra test has been added to avoid leaving GET /users/me/alert_words
too untested.
Querying an endpoint with no information (thus a noop) and it producing
a successful response doesn't seem to be expected.
Given the case that the client makes such query with no content it will
probably be unintentional and the API should let them know about it.
Revert to the use of `do_add_alert_words()` in `add_alert_words()`
instead of `do_set_alert_words()` since it is used for serving a
PUT request. This change seems to be mistakenly done in commit
`d564a76f8e45b24cd2c66475ef7693582fb2f5fc'.
For a long time, rest_dispatch has had this hack where we have to
create a copy of it in each views file using it, in order to directly
access the globals list in that file. This removes that hack, instead
making rest_dispatch just use Django's import_string to access the
target method to use.
[tweaked and reorganized from acrefoot's original branch in various
ways by tabbott]