This resolves a long-standing issue:
we could not use proper include paths for test-helper code that was defined alongside the tests.
Since some test-helper code must now be relocated into the »Vault«-Layer,
I took the opportunity to finally resolve this annoyance. The solution is two-fold
* introduce a dedicated test-support library
* remove the quirks that were necessary to support some plain-C tests
Together, this allows to raise the include-directory by one level,
and then to adjust all folder names so that they match the namespace
the buildsystem will now pick up and link
all test cases according to the layer, e.g.
backend tests will automatically be linked
against the backend + library solely.
Using a policy based switch in case the client
interface collaborates and provides copy operations;
in this case, a direct static downcast instead of
the expensive indirect (dynamic) cast to the
management interface can be employed.
