Fix warnings in dtwm

- Improve pointer/int compatibility
- Include unpublished Dt headers in Dt
- Use <Xm/XmPrivate.h> for unpublished Motif functions

There are still warnings left generated because
ElementValue.parsed_value should really be a union.

There are also some warnings left because of XtPointer
casting and some unused variables and functions.

cde/programs/dtwm/WmCDecor.c

@@ -1107,7 +1107,7 @@ void GetTextBox (ClientData *pcd, XRectangle *pBox)
 {
     int x,y;
     unsigned int width,height;
-#ifdef WSM
+#if defined(WSM) && defined(DT_LEFT_JUSTIFIED_TITLE)
     Dimension textWidth;
     Dimension offset;
     XmFontList  fontList;