Support optional message in backend cancellation/termination

When Who What
2018-10-01 08:49:34 Daniel Gustafsson (d_gustafsson) Added annotation "The request for backend signal code refactoring (patch 1) " to 20180124154548.gmpyvkzlsijren7u@alvherre.pgsql
2018-04-09 00:47:29 Michael Paquier (michael-kun) Closed in commitfest 2018-03 with status: Returned with feedback
2018-03-20 11:12:43 Eren Basak (aamederen) Added aamederen as reviewer
2018-01-24 13:58:06 Daniel Gustafsson (d_gustafsson) Changed authors to Daniel Gustafsson (d_gustafsson)
2018-01-24 13:58:06 Daniel Gustafsson (d_gustafsson) Changed reviewers to Yugo Nagata (yugo.nagata)
2018-01-24 13:57:35 Daniel Gustafsson (d_gustafsson) Attached mail thread C2C7C3EC-CC5F-44B6-9C78-637C88BD7D14@yesql.se
2018-01-24 13:57:34 Daniel Gustafsson (d_gustafsson) Created patch record