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/tcl_bx.h

@@ -3,9 +3,8 @@
  * CopyRight Colten Edwards Oct 96
  *
  */
-
-#ifndef _IRCTCL_H
-#define _IRCTCL_H
+#ifndef TCL_BX_H_
+#define TCL_BX_H_
 
 int handle_dcc_bot (int, char *);
 int handle_tcl_chan (int, char *, char *, char *);