Now that @basictag is becoming deprecated in Djblets 0.10, we are

migrating all usage of @basictag to Django's @Library.simple_tag

decorator. To ensure that everything works correcty, unit tests have

been added to test all tags that previously used @basictag to

ensure that they will continue to render correctly.
Several testing utilities have been added in this patch to facilitate

this migration. First off is the MemoryTemplateLoader, which loads

template sources from an in-memory string. This is to be used in

conjunction with the context managers provided by

djblets.template.loaders.util:

add_template_loader, which temporarily adds a template source

  loader; and
replace_template_loaders, which temporarily replaces all the

  template source loaders.

Ran unit tests.