buf_flush_buffered_writes(): Remove bogus assertion failure.

page_header_reset_last_insert(): Add page_zip parameter.
rec_get_next_ptr(): Return a pointer to the same page, or NULL.
page_dir_delete_slot(): Fix off-by-one errors.

Fix some (not all) bugs found by testing.

Fix bugs found during testing.

Add page_zip parameter to page_dir_slot_set_rec().
Improve the documentation of the page_zip parameters in page0page.
Add function page_trailer_get_len().

Slightly improve error handling.

Implement page_zip_write_header().
Add page_zip parameter to btr_page_set_ functions.
Allow page_copy_rec_list_end() to be called with invalid new_page_zip
if the page has been newly created.

Initial import of the zip-like compression of B-tree pages.