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/TermPrimPendingText.c

@@ -278,7 +278,7 @@ _DtTermPrimPendingTextFlush
     walkPendingText(list);
 #endif	/* DEBUG */
     
-    while (chunk = _DtTermPrimPendingTextGetChunk(list)) {
+    while ((chunk = _DtTermPrimPendingTextGetChunk(list))) {
 	(void) _DtTermPrimPendingTextRemoveChunk(list, chunk);
     }
 }