Standardise header include guards

Tokens that begin with two underscores __* or an underscore and an uppercase letter _X* are reserved,
so we should avoid those for our own include guards.  The standard I'm settling on for foo.h is FOO_H_.

include/hold.h

@@ -9,9 +9,8 @@
  *
  * @(#)$Id$
  */
-
-#ifndef __hold_h_
-#define __hold_h_
+#ifndef HOLD_H_
+#define HOLD_H_
 
 	void	remove_from_hold_list (Window *);
 	void	add_to_hold_list (Window *, char *, int);
@@ -22,4 +21,4 @@
 	int	hold_queue_logged (Window *);
 	void	toggle_stop_screen (char, char *);
 
-#endif /* __hold_h_ */
+#endif /* HOLD_H_ */