Create dir.h to declare functions defined in dir.c

Update files that depend on dir functions to include dir.h
Declare as static all functions in dir.c that are not needed externally.
Add dependencies to makefile-tail.

	modified:   bin/makefile-tail
	new file:   inc/dir.h
	modified:   src/dir.c
	modified:   src/dsk.c
	modified:   src/main.c
	modified:   src/subr.c
	modified:   src/vmemsave.c

src/main.c

@@ -23,6 +23,7 @@ static char *id = "$Id: main.c,v 1.4 2001/12/26 22:17:03 sybalsky Exp $ Copyrigh
 #include "lispemul.h"
 #include "dbprint.h"
 #include "unixfork.h"
+#include "dir.h"
 
 #include <sys/types.h>
 #ifndef DOS