* dgud/mnesia/checkpoint-crash/OTP-14841:
  mnesia: Fix checkpoint crash

* dgud/mnesia/slow-startup/OTP-14829:
  mnesia: Read schema user properties directly

Bad timing can cause retain messages to go to a new process if
checkpoint name is reused directly and the checkpoints contain
different tables.

Ignore those messages instead of crash.

* hans/ssh/openssh_client_pubkey_sha2/ERL-531/OTP-14827:
  ssh: Special treatment of OpenSSH clients >= 7.2 rsa-sha2-* public keys

Thoose clients signs with sha instead of sha2-*.  Try first to verify with the correct one, and if that fails, retry with sha1.

Doing a proper transaction handling of user properties (in current
implmenentation) caused schema_transactions to be quadratic which
caused huge startup times for nodes with many tables since the merge schema
is a schema_transaction.

Do a direct read instead, cheap but implies that the plugin changes
will not be visible until the changes are commited and cannot be used
later in same transaction, which was possible before if undocumented
functions where used.