+/* The following #include avoids a potential problem when Gnulib substitutes
+ * for close() by putting "#define close rpl_close" into <unistd.h>, by
+ * ensuring that every source file that includes this one sees the #define..
+ * (It would probably be better to rename the 'close' member of struct
+ * ctl_class.) */
+#include <unistd.h>
+