v4.2.2

commit 71dc4288d409685aeebbfba52034354234e3f7d7
Author: Victor Lowther <victor.lowther@gmail.com>
Date:   Mon Jan 27 10:30:25 2020 -0600

    Handle transaction lock checking corner case where acquireWrite can deadlock due to pending reads

M   backend/tx.go
M   backend/tx_test.go

End of Note