page_mem_alloc_free(), page_dir_set_n_heap(), page_ptr_set_direction():
Merge with the callers.

page_direction_reset(), page_direction_increment(),
page_zip_dir_insert(), page_zip_write_rec_ext(), page_zip_write_rec():
Add the parameter mtr, and write log.

PageBulk::insert(), PageBulk::finish(): Write log for all changes.

page_cur_rec_insert(), page_cur_insert_rec_write_log(),
page_cur_insert_rec_write_log(): Remove.

page_rec_set_next(), page_header_set_field(), page_header_set_ptr():
Remove. Use lower-level operations with or without logging.

page_zip_dir_add_slot(): Move to the same compilation unit with
its only caller, page_cur_insert_rec_zip().

page_cur_insert_rec_zip(): Mark pieces of code that must be skipped
once this task is completed.

btr_defragment_chunk(): Before starting a mini-transaction that
is writing (a lot), invoke log_free_check(). This should allow
the test innodb.innodb_defrag_concurrent to pass with the
mtr default_mysqld.cnf setting of innodb_log_file_size=10M.

MLOG_BUF_MARGIN: Remove.