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/numbers.h

@@ -9,11 +9,10 @@
  *
  * @(#)$Id$
  */
-
-#ifndef __numbers_h_
-#define __numbers_h_
+#ifndef NUMBERS_H_
+#define NUMBERS_H_
 
 char *numeric_banner(void);
 void numbered_command(char *, int, char **);
 		
-#endif /* __numbers_h_ */
+#endif /* NUMBERS_H_ */