Various changes prompted by my boss taking an interest:

Various changes prompted by my boss taking an interest:
 - added a compilation option -DSTANDALONE_SOLVER which makes both
   of Solo's internal solvers accessible from the command line.
 - fix a bug in nsolve turned up by testing in this mode: it failed
   to iterate at all! Oddly, this massive improvement to the
   effectiveness of nsolve hasn't emptied the generated grids by
   very much.
 - add an extra mode of reasoning to my to-do list (which is the
   dual of one already there, so I'm kicking myself).

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@5670 cda61777-01e9-0310-a592-d414129be87e