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/dcc.h

@@ -4,9 +4,8 @@
  * Copyright(c) 1998 Colten Edwards 
  *
  */
-
-#ifndef __dcc_h_
-#define __dcc_h_
+#ifndef DCC_H_
+#define DCC_H_
 
 #include "struct.h"
 
@@ -172,4 +171,4 @@ struct dcc_offer {
 	
 #define DCC_STRUCT_TYPE  0xdcc0dcc0
 
-#endif /* __dcc_h_ */
+#endif /* DCC_H_ */