* dgud/mnesia/sticky-bug/ERL-768/OTP-15979:
  mnesia: Bump protocol version
  mnesia: Introduce sync_asym_trans protocol

Remove unsupported conversions from the old protocols.
This means mnesia on OTP-R18 nodes is no longer able to connect to
OTP-22 mnesia nodes.

Add protocol conversion for old nodes and sync_asym_trans transactions.

Transactions with sticky locks could with async_asym transactions be
committed in the wrong order, since asym transaction are spawned on
the remote nodes.

See ERL-768.

If add_table_copy was called when a node was starting it deadlock
waiting for mnesia_controller, when schema was not merged.

Abort if that is the case.

If an activity function fails with an error, the stacktrace is
dropped in non_transaction function try/catch clause.
This makes debuging of errors inside a transaction really hard.

Transaction activities handle errors and exits differently, non-transaction
activities should do the same.

Adding the stacktrace to the exit reason when translating errors to exits.

- first stab at fixing index_[read|match_object] w plugins
- do not include index plugins at match ops
- add index_plugin_test_suite
- Increase ix plugin test coverage + bug fix

* maint-20:
  Updated OTP version
  Prepare release
  Updated the engine load functionality
  Clean up bag index tables

Conflicts:
	OTP_VERSION
	lib/crypto/c_src/crypto.c
	lib/crypto/doc/src/notes.xml
	lib/crypto/vsn.mk
	lib/mnesia/doc/src/notes.xml
	lib/mnesia/vsn.mk
	otp_versions.table

Index records for bag tables with ram_copies was not deleted
after "real" objects where deleted and thus a memory leak.

* upstream/pr/1858:
  Fix delete_object and write convergence in transaction.

OTP-15231