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/TermPrimSelect.h

@@ -277,6 +277,41 @@ void
 _DtTermPrimSelectInitBtnEvents(
         Widget w);
 
+extern
+void
+_DtTermPrimRenderRefreshTextLinear
+(
+    Widget          w,
+    XmTextPosition  start,
+    XmTextPosition  stop
+);
+
+extern
+XmTextPosition
+rowColToPos
+(
+    DtTermPrimitiveWidget   tw,
+    short                   row,
+    short                   col
+);
+
+extern
+void
+_DtTermPrimSelectDisown
+(
+    Widget          w
+);
+
+extern
+Boolean
+_DtTermPrimSelectIsInSelection
+(
+    Widget      w,
+    int         row,
+    short       startCol,
+    short       width,
+    short      *selWidth
+);
 
 #ifdef	__cplusplus
 } /* close scope of 'extern "C"'... */