added some missing CAP_SOLV guards

cell.cpp

@@ -913,7 +913,9 @@ EX int heptdistance(heptagon *h1, heptagon *h2) {
   #if CAP_CRYSTAL
   if(cryst) return crystal::space_distance(h1->c7, h2->c7);
   #endif
+  #if CAP_SOLV
   if(sol) return solv::approx_distance(h1, h2);
+  #endif
   while(true) {
     if(h1 == h2) return d;
     for(int i=0; i<S7; i++) if(h1->move(i) == h2) return d + 1;