Comment 1 for bug 837537

In versions before 5.1.7 external pages have type FIL_PAGE_INDEX.

/** File page types (values of FIL_PAGE_TYPE) @{ */
#define FIL_PAGE_INDEX 17855 /*!< B-tree node */
#define FIL_PAGE_UNDO_LOG 2 /*!< Undo log page */
#define FIL_PAGE_INODE 3 /*!< Index node */
#define FIL_PAGE_IBUF_FREE_LIST 4 /*!< Insert buffer free list */
/* File page types introduced in MySQL/InnoDB 5.1.7 */
#define FIL_PAGE_TYPE_ALLOCATED 0 /*!< Freshly allocated page */
#define FIL_PAGE_IBUF_BITMAP 5 /*!< Insert buffer bitmap */
#define FIL_PAGE_TYPE_SYS 6 /*!< System page */
#define FIL_PAGE_TYPE_TRX_SYS 7 /*!< Transaction system data */
#define FIL_PAGE_TYPE_FSP_HDR 8 /*!< File space header */
#define FIL_PAGE_TYPE_XDES 9 /*!< Extent descriptor page */
#define FIL_PAGE_TYPE_BLOB 10 /*!< Uncompressed BLOB page */
#define FIL_PAGE_TYPE_ZBLOB 11 /*!< First compressed BLOB page */
#define FIL_PAGE_TYPE_ZBLOB2 12 /*!< Subsequent compressed BLOB page */
/* @} */