Patch: pg_stat_statements: query, session, and eviction identification

https://commitfest.postgresql.org/action/patch_view?id=1227
http://archives.postgresql.org/message-id/CABzZFEuaHsCq2JG313G__V6H+knn9h+WKeBMuLWkz-Py=dKcuw@mail.gmail.com