Log Message:
-----------
Add explanatory detail to Hot Standby cancelation error messages
with errdetail(). Add errhint() to suggest retry in certain cases.
Modified Files:
--------------
pgsql/src/backend/tcop:
postgres.c (r1.586 -> r1.587)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/tcop/postgres.c?r1=1.586&r2=1.587)