Change to the handling of -DCOMBINED in the makefiles. Instead of

Change to the handling of -DCOMBINED in the makefiles. Instead of
defining it centrally per port, I think it's neater to define it for
each puzzle when adding that puzzle to the ALL list - because those
front ends which take -DCOMBINED are precisely those which use ALL.
In particular, this change opens up the possibility of compiling
both individual puzzles _and_ a combined monolith within the same
makefile.

[originally from svn r8178]