"In principle" setting `SCRIPT_NAME` is enough. The way we do this is [1] using
`FORCE_SCRIPT_NAME` (which does not depend on messing with reverse proxy
settings and [2] by deducing the correct value from `BASE_URL` (which must be
set anyway) automatically.
By works I mean: `reverse` and `{% url` pick it up from there.
However, there are subtleties / extra work:
* `STATIC_URL` is needed too b/c https://code.djangoproject.com/ticket/34028
* in many pre-existing code I just created a path manually in the html. Such
hrefs are obviously not magically fixed for script_name. Rather than doing
the "full rewrite" (into `{% url`) this commit just prepends the
`script_name` in those cases. That's the way forward that will least likely
break and it gives us something to grep for if we ever want to 'do it
right'.
* `LOGIN_REDIRECT_URL` and `LOGIN_URL` needed to use a view-name for this to
work (using a view-name gets revolved using the thing that introduces
`script_name`)
Checked, no work needed:
* views (`redirect` and `HttpResponseRedirect`)
* html uses of action="..."
Fix#93
