The prior attempt at fixing packaging appeared to work, but was due to

some stale generated files that ended up in an include path. This fixes

the packaging properly.
STATIC_ROOT wasn't actually meshing well with the include path. The

include path now points to the static/ directory instead of

static/djblets/, and STATIC_ROOT now expands to an empty string. This

allows an import like @{STATIC_ROOT}/djblets/ to match djblets/

within Djblets's static/ directory.
This also means that, while we can safely use STATIC_ROOT for imports,

we cannot use it for anything that will expand within the .css output

(such as image URLs).

Started from a completely fresh environment, and generated a suitable

package.