Note: not fixing all relevant warnings.
Especially, the "-Woverloaded-virtual" of Clang defeats the whole purpose
of generated generic interfaces. For example, our Variant type is instantiated
with a list of types the variant can hold. Through metaprogramming, this
instantiation generates also an embedded Visitor interface, which has
virtual 'handle(TY)' functions for all the types in question
The client now may implement, or even partially implement this Visitor,
to retrieve specific data out of given Variant instance with unknown conent.
To complain that some other virtual overload is now shaddowed is besides the point,
so we might consider to disable this warning altogether
Actually I arried at the conclusion, that the *receiving* of
a diff representation is actually a typical double-dispatch situation.
This leads to the attempt to come up with a specialised visitor
as standard pattern to handle and apply a diff. Obviously,
we do not want the classical GoF-Visitor, but (yes, we had
that discussion allready) -- well in terms of runtime cost,
we have to deal with at least two indirections anyway;
so now I'm exploring the idea to implement one of these
indirections through a functor object, which at the same time
acts as "Tag" in the diff representation language (instead
of using an enum as tag)
- the tests covering threadind support and object monitors
are located in the backend test-library and linked against liblumierabackend.so
- some fundamental facilities of proc-layer moved from the library tree
into the basic components tree, since *testing* them requires at least
to link against liblumieracommon.so
