instead of doing multiple passes over the submodules, do everything in
one go.

as a bonus, as the internal structure uses exclusion entries in the
module list, we can make that feature user-accessible just as well.

Change-Id: I8bfb30c8051a9150f92e2e124ff52f64e3efe03c
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>