We had to cap django-pipeline to 1.6.9 to work around a caching bug that

was fixed in 1.6.10. After the release of 1.6.10, we never upgraded

pipeline, and over time this exposed a new problem that affected new

virtual environments. To efficiently compile static media bundles,

pipeline uses the futures module, but if this isn't available, it

compiles one at a time, serially.
The problem was that, until 1.6.14, pipeline was conditionally adding

futures as a dependency when building on Python < 3.2, but the

pre-built wheels were built on a newer 3.x release, causing the

dependency to be dropped and causing compilation to be slow.
This change bumps to 1.6.14, fixing the old caching issue and the new

dependency issue.

Installed the new version and then re-built Review Board packages. Saw

that the speed penalty I noticed went away, and that multiple files were

being compiled at the same time.