Kill most warnings in lib/DtTerm.

Mostly missing headers, explicit parentheses and new prototypes.

Some Caveats:
* I haven't compile-tested the SVR4 getpty file, it might need another tweak
* There were operator precedence bugs in TermPrimCursor.c and TermPrimRender.c
  (^ vs. !=).  This might change behaviour, but at least I haven't experienced
  any crashes ...
* This adds a little more dependencies for include ordering, but unless we
  want to play the "headers that include headers that include headers..." game,
  this is unavoidable.

cde/lib/DtTerm/TermPrim/TermPrimParser.c

@@ -36,6 +36,7 @@ static char rcs_id[] = "$TOG: TermPrimParser.c /main/2 1999/10/15 12:23:41 mgree
  * (c) Copyright 1996 Hitachi.						*
  */
 
+#include <Xm/Xm.h>
 #include "TermPrimDebug.h"
 #include "TermPrimP.h"
 #include "TermPrimParserP.h"