page_zip_parse_write_blob_ptr(): New function for applying the redo log
record MLOG_ZIP_WRITE_BLOB_PTR.

page_zip_write_blob_ptr(): Write the necessary information to the redo log.

page0zip.c: Tighten the assertions to ensure that blob_ptr < page_zip->n_blobs.

page_zip_write_node_ptr(): Use memcpy() instead of mach_write_to_4().