check_dig: stick with integer devision

This change saves us from having to link check_dig against "libm"

plugins/check_dig.c

@@ -90,7 +90,7 @@ main (int argc, char **argv)
     usage_va(_("Could not parse arguments"));
 
   /* dig applies the timeout to each try, so we need to work around this */
-  int timeout_interval_dig = ceil((double) timeout_interval / (double) number_tries);
+  int timeout_interval_dig = timeout_interval / number_tries + number_tries;
 
   /* get the command to run */
   xasprintf (&command_line, "%s @%s -p %d %s -t %s %s %s +tries=%d +time=%d",