rec_get_offsets_reverse(): Calculate extra_size correctly.

page_zip_apply_log(): Fix an off-by-one error in comparison.
Replace heap_status with hs where possible.
Increment the heap_no in heap_status correctly.

page_zip_decompress(): Eliminate the local variable "err".
Check for Z_STREAM_END only at the start of a record, so that
incomplete records will always be detected.

page_zip_write_rec(): Calculate the address of "storage" in the
same way as elsewhere.  Add TODO comments regarding the handling
of the uncompressed fields (BLOB pointers, trx_id, and roll_ptr).