Files should explicitly include the definitions they directly depend on (#355)

... start by fixing the include files and the fallout in C source from
removing includes not directly needed by headers that previously included
them.

inc/mvsdefs.h

@@ -1,6 +1,7 @@
 #ifndef MVSDEFS_H
 #define MVSDEFS_H 1
-#include "stack.h"
+#include "lispemul.h" /* for LispPTR */
+#include "stack.h" /* for FX2 */
 LispPTR make_value_list(int argcount, LispPTR *argarray);
 void simulate_unbind(FX2 *frame, int unbind_count, FX2 *returner);
 LispPTR values(int arg_count, register LispPTR *args);