lua: add missing include files

These are actually already included in osdep/io.h, but I think it's
cleaner to repeat them in the file where they are actually needed.
(osdep/io.h needs to have them for other reasons.)

player/lua.c

@@ -18,6 +18,8 @@
 #include <assert.h>
 #include <string.h>
 #include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
 #include <dirent.h>
 #include <math.h>