fix handling of d_name in struct dirent

basically there are 3 choices for how to implement this variable-size
string member:
1. C99 flexible array member: breaks using dirent.h with pre-C99 compiler.
2. old way: length-1 string: generates array bounds warnings in caller.
3. new way: length-NAME_MAX string. no problems, simplifies all code.

of course the usable part in the pointer returned by readdir might be
shorter than NAME_MAX+1 bytes, but that is allowed by the standard and
doesn't hurt anything.

include/dirent.h

@@ -18,7 +18,7 @@ struct dirent
 	off_t d_off;
 	unsigned short d_reclen;
 	unsigned char d_type;
-	char d_name[1];
+	char d_name[256];
 };
 
 #define d_fileno d_ino