Symmetry reduction slow when centers given first

[rokicki]

On the 3x3x3, if you include centers and give them first, execution will be nearly 4x slower than if you give edges or corners first. This is because an optimization to find the least lexical symmetry representative does not work if the pieces are not permuted by moves. A workaround is just to ensure centers are not given first, but it would be nice if twsearch would work as well no matter the order of the given sets.