dtwm: Cleanup some implicit definitions

Mostly this is adding appropriate #includes and declarations,
but for WmImage.c we also change from using the proper name
for XmeGetMask, rather than the identical but renamed
version _DtGetMask which is not exported in any header.

cde/programs/dtwm/WmInitWs.c

@@ -59,6 +59,7 @@ static char rcsid[] = "$TOG: WmInitWs.c /main/18 1999/09/20 15:18:22 mgreess $"
 #include <X11/Xos.h>
 #include <X11/cursorfont.h>
 #include <Xm/Xm.h>
+#include <Xm/AtomMgr.h>
 #include <X11/Shell.h>
 #include <X11/Core.h>
 #include <X11/keysym.h>
@@ -78,6 +79,7 @@ typedef struct
 #ifdef WSM
 #include <Dt/GetDispRes.h>
 #include <Dt/SessionP.h>
+#include <Dt/SessionM.h>
 #include <Dt/DtP.h>
 #include <Dt/Message.h>
 #include <Dt/WsmM.h>
@@ -2677,6 +2679,8 @@ VirtKeys4DIN(
   if(    !prop_existed    )
     {
       bindingsString = NULL ;
+      /* FIXME: this is an unexported openmotif procedure */
+      extern void _XmVirtKeysLoadFallbackBindings(Display *dsp, String *binding);
       _XmVirtKeysLoadFallbackBindings( dsp, &bindingsString) ;
       XtFree( bindingsString) ;