Ensure namespace package is installed.

This is a workaround for bug 1194742. There is actually a bug in
upstream d2to1 that has a PR up:

https://github.com/iguananaut/d2to1/pull/32

But until that is released, this should fix the immediate problem.

Change-Id: I136b8493c8d8d48a0116facf5f23c2a1479c070f
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>