Fix commit 0aefbaf7, which caused no plugins to be found at runtime

CCMAIL: cgiboudeaux@gmx.com
Christophe, thanks for commit 0aefbaf7 but please do not commit straight
away to a stable branch! Run things through reviewboard first. This
commit broke the application, failed the unit tests, made Jenkins cry
and missed a follow-up commit to master to ensure the branches were in
sync.

(cherry picked from commit 79522b5b)