Fail BRIN control functions during recovery explicitly

They already fail anyway, but prior to this patch they raise an ugly
error message about a lock that cannot be acquired.  This just improves
the message.

Author: Masahiko Sawada
Reported-by: Masahiko Sawada
Discussion: https://postgr.es/m/CAD21AoBZau4g4_NUf3BKNd=CdYK+xaPdtJCzvOC1TxGdTiJx_Q@mail.gmail.com
Reviewed-by: Kuntal Ghosh, Alexander Korotkov, Simon Riggs, Michaël Paquier, Álvaro Herrera

Author: alvherre

src/backend/access/brin/brin.c

@@ -788,6 +788,12 @@ brin_summarize_new_values(PG_FUNCTION_ARGS)
 	Relation	heapRel;
 	double		numSummarized = 0;
 
+	if (RecoveryInProgress())
+		ereport(ERROR,
+				(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
+				 errmsg("recovery is in progress"),
+				 errhint("BRIN control functions cannot be executed during recovery.")));
+
 	/*
 	 * We must lock table before index to avoid deadlocks.  However, if the
 	 * passed indexoid isn't an index then IndexGetRelation() will fail.