Silence lots of warnings in lib/DtHelp.

* 64bit warnings
* Missing prototypes
* explicit parentheses / brackets

There's still some work to be done, but, as always, it's a start ...

cde/lib/DtHelp/GifUtils.c

@@ -71,6 +71,7 @@
 #include <string.h>
 #include <math.h>
 #include <assert.h>
+#include <Xm/XmPrivate.h>
 #include "GifUtilsI.h"
 
 #ifndef __STDC__