Cleanups to Solo:

 - use the new `shuffle' utility function in a couple of places
 - remove the random_state parameter from solver(). It was there
   because I initially wanted to use the same solver for grid
   generation, but since I had to abandon that plan the solver now
   doesn't have any need for randomness at all.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@6093 cda61777-01e9-0310-a592-d414129be87e