Patch: pg_stat_statements: query, session, and eviction identification

https://commitfest.postgresql.org/action/patch_view?id=1227
http://archives.postgresql.org/message-id/CABzZFEvXqOw_969+QaG=qH9W4yd+fW3keSTg7c1MiThwndagsw@mail.gmail.com