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/TermView/TermView.c

@@ -41,6 +41,7 @@ static char rcs_id[] = "$XConsortium: TermView.c /main/1 1996/04/21 19:20:13 drk
 #include "TermViewP.h"
 #include <Xm/ScrolledW.h>
 #include <Xm/ScrollBar.h>
+#include <Xm/DrawP.h>
 #include <Xm/Form.h>
 #include <Xm/PushB.h>
 #include <Xm/PushBG.h>
@@ -601,7 +602,7 @@ externaldef(termclassrec) DtTermViewClassRec dtTermViewClassRec =
     {
 	NULL,
 	0,
-	NULL,
+	0,
 	NULL,
 	NULL,
 	NULL,