Add some basic definitions for a future htree implementation.

MFC after:	3 days

sys/fs/ext2fs/ext2_dinode.h

@@ -57,10 +57,12 @@
 #define EXT2_COMPR		0x00000004	/* Compress file */
 #define EXT2_SYNC		0x00000008	/* Synchronous updates */
 #define EXT2_IMMUTABLE		0x00000010	/* Immutable file */
-#define EXT2_APPEND		0x00000020	/* writes to file may only append */
+#define EXT2_APPEND		0x00000020 /* writes to file may only append */
 #define EXT2_NODUMP		0x00000040	/* do not dump file */
 #define EXT2_NOATIME		0x00000080	/* do not update atime */
 
+#define EXT2_HTREE		0x00001000	/* HTree-indexed directory */
+
 /*
  * Definitions for nanosecond timestamps.
  * Ext3 inode versioning, 2006-12-13.

sys/fs/ext2fs/ext2fs.h

@@ -210,6 +210,7 @@ struct m_ext2fs {
 #define EXT2F_COMPAT_PREALLOC		0x0001
 #define EXT2F_COMPAT_HASJOURNAL		0x0004
 #define EXT2F_COMPAT_RESIZE		0x0010
+#define EXT2F_COMPAT_HTREE		0x0020
 
 #define EXT2F_ROCOMPAT_SPARSESUPER	0x0001
 #define EXT2F_ROCOMPAT_LARGEFILE	0x0002