Add performance statistics to path finder

New function path_find_print_stats() prints a few numbers of interest
when compiled with PATH_FIND_STATS defined.

src/lib/update/finish.c

@@ -130,4 +130,5 @@ assemble_dist_paths(double *import_cost)
 				   sp->sct_x, sp->sct_y,
 				   dist->sct_own, MOB_MOVE);
     }
+    path_find_print_stats();
 }