Crash gracefully on start-up if the user compiled with cooling but forgot the runtime flag.

Fixes #571 (closed)

examples/main.c

@@ -742,12 +742,19 @@ int main(int argc, char *argv[]) {
     if (myrank == 0) potential_print(&potential);
 
     /* Initialise the cooling function properties */
-    bzero(&cooling_func, sizeof(struct cooling_function_data));
-    if (with_cooling || with_temperature) {
 #ifdef COOLING_NONE
-      if (with_cooling)
-        error("ERROR: Running with cooling but compiled without it.");
+    if (with_cooling || with_temperature) {
+      error("ERROR: Running with cooling / temperature calculation"
+	    " but compiled without it.");
+    }
+#else
+    if (!with_cooling && !with_temperature) {
+      error("ERROR: Compiled with cooling but running without it. "
+	    "Did you forget the --cooling or --temperature flags?");
+    }
 #endif
+    bzero(&cooling_func, sizeof(struct cooling_function_data));
+    if (with_cooling || with_temperature) {
       cooling_init(params, &us, &prog_const, &cooling_func);
     }
     if (myrank == 0) cooling_print(&cooling_func);