Patches from Richard B for Solo:

Patches from Richard B for Solo:
 - prevent highlighting a clue square at all
 - enable easier switching between highlight types by not requiring
   a left-click highlight to be left-click-cancelled before
   right-clicking, and vice versa
 - fix bit-rot in -DSTANDALONE_SOLVER
Also one of mine:
 - replicate Richard's -DSTANDALONE_SOLVER fix in Pattern, where it
   was also broken.

[originally from svn r5892]