let's tame jQuery imports

[evildmp]

These two tiny changes have saved me from a world of pain and misery. I actually cried because of the problems that this pull request addresses.

The changes do two things:

PlaceholderAdmin(ModelAdmin).Media

Summary: stop importing jquery.js.min in PlaceholderAdmin(ModelAdmin).Media.

Django's own ModelAdmin already calls in jQuery; so we shouldn't try to import the same thing. (I say 'try' because actually we don't even do that correctly - see the second paragraph at #1584.)

Importing jquery.js.min breaks attempts to make one's own admin/base_site.html provide a newer jQuery where it's needed.

cms/templates/admin/cms/page/plugin_change_form.html

Summary: create a {% block jquery %} around <script type="text/javascript" src="{% admin_static_url %}js/jquery.min.js"></script> in cms/templates/admin/cms/page/plugin_change_form.html.

A similar issue. The plugin_change_form.html extends admin/base_site.html, and loads jQuery. Now suppose your plugin needs a newer jQuery - there is no way to make that work without removing the jQuery here.

By putting it in a {% block jquery %}, it's now possible for your plugin's form to point at a template that extends plugin_change_form.html and overrides that block with the jQuery you want. Or, if your own admin/base_site.html already imports the jQuery you need, a simple {% block jquery %}{% endblock %} will prevent the undesired one from being loaded.

Breaks no tests, though I'm not sure how to test for this exactly. Works in practice as described above, on both a PlaceholderAdmin-based admin, and on a plugin.

Saved me from tears.

[FinalAngel]

looks good to me!

[evildmp]

OK, don't merge this just yet, I'll add something for the documentation.

[FinalAngel]

docs also look fine to me :)