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/log.h

@@ -9,9 +9,8 @@
  *
  * @(#)$Id$
  */
-
-#ifndef __log_h_
-#define __log_h_
+#ifndef LOG_H_
+#define LOG_H_
 
 	void	do_log (int, char *, FILE **);
 	void	logger (Window *, char *, int);
@@ -19,4 +18,4 @@
 	void	BX_add_to_log (FILE *, time_t, const char *, int mangler);
 
 
-#endif /* __log_h_ */
+#endif /* LOG_H_ */