dtype_new_read_for_order_and_null_size(): Correctly assign type->prtype.
This caused the fatal error and crash.

ibuf_merge(): Relax a too strict condition that would result in
[ERROR] InnoDB: Unable to upgrade the change buffer
when there exist buffered changes to redundant secondary indexes, such as
PRIMARY KEY(x), INDEX(x).

ibuf_upgrade(): Modify at most one user tablespace per mini-transaction,
to be crash-safe.

page_cur_insert_rec_zip(), page_cur_delete_rec(): Relax debug assertions
for ibuf_upgrade().

ibuf_log_rebuild_if_needed(): Invoke recv_sys.debug_free() only after
srv_log_rebuild_if_needed() to avoid an assertion failure. This code
is executed when the innodb_log_file_size is changed when upgrading
from 10.x to 11.0.

Tested by: Matthias Leich, Christian Hesse