cuddUniqueConstant: get rid of valgrind's warning.
cuddUniqueConstant: get rid of valgrind's warning.

cuddUniqueConstant() function uses hack union that is used for correctly
hashing doubles etc. The union is now filled correctly to avoid valgrind's
warnings about accessing uninitialized memory.

ondrik/cudd4libsfta,ondrik/cudd4libsfta,ondrik/cudd4libsfta