wibble: Make Preferred's constructor constexpr when compiling with C++11.
serialization: Rework serialization for better flexibility.
We can now serialize all fundamental (integral, floating-point and bool)
types, tuples, tuple convertible types and (varibale sized)
containers with arbitrary nesting (that is something like:
std::vector< std::tuple< std::deque< int >, long, double > >).
io: Fix compilation with fake IO (match changes in real IO).
test: Print offending values in assert_{eq,neq,leq,lt}.