Issue with postgres 11beta2 and powa on debian stretch amd64

Hello,

I installed postgresql-11-powa on a fresh debian stretch amd64 with
postgresql-11 beta2

I got several errors "set-valued function called in context that cannot accept a
set" which should be fixed :
2018-07-22 14:16:22.209 CEST [30135] WARNING:  powa_take_snapshot(): function
"powa_user_functions_snapshot" failed:
                      state  : 0A000
                      message: set-valued function called in context that cannot
accept a set
                      detail :
                      hint   :
                      context: SQL statement "WITH func(dbid, r) AS (
                SELECT oid,
                    powa_stat_user_functions(oid)
                FROM pg_database
            )
            INSERT INTO powa_user_functions_history_current
                SELECT dbid, (r).funcid,
                ROW(now(), (r).calls,
                    (r).total_time,
                    (r).self_time)::powa_user_functions_history_record AS record
                FROM func"
        PL/pgSQL function powa_user_functions_snapshot() line 10 at SQL statement
        SQL statement "SELECT powa_user_functions_snapshot()"
        PL/pgSQL function powa_take_snapshot() line 76 at EXECUTE
        SQL statement "SELECT powa_take_snapshot()"


FYI, I do not have this error if I build powa from github's sources. So, I seems
it is a packing issue.

Thanks

--
Adrien NAYRAT