"old" == "gcc 4.4". the standard c++ library of this compiler seems to
invoke the copy operator when creating objects in a vector, whereas
newer versions of the library don't. The problem is that std::unique
pointer cannot be copied because it is -- err -- unique and thus the
implicit copy operator for the SatFuncMultiplexer class gets deleted
by the compiler.
the fix is to introduce a "fake" copy operator which does not do
anything but is present to make std::vector of stdlibc++-4.4
happy. this is obviously not very elegant, but I could not come up
with a better solution. (another fix would be to use raw pointers
instead of std::unique_ptr, but IMO this does not qualify as
"better".)