Currently useless. Catkin seems to expect all include directories (INCLUDE_DIRS in catkin_package) to be relative to the package root (CMAKE_CURRENT_SOURCE_DIR). QpOASES actual files get checked out into the build tree though.
Python library
Will end up as qpoases in the workspace scope (so do import qpoases). After a build you should be able to run the Python examples. Examples get checked out during the build process and end up (relative to your workspace) in