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

inc/dir.h

@@ -0,0 +1,10 @@
+#ifdef DOS
+int make_old_version(char *old, char *file);
+#endif
+#ifdef FSDEBUG
+void print_finfo(FINFO *fp);
+#endif
+int init_finfo();
+LispPTR COM_gen_files(register LispPTR *args);
+LispPTR COM_next_file(register LispPTR *args);
+LispPTR COM_finish_finfo(register LispPTR *args);