Move Trigger and TriggerDesc structs out of rel.h into a new reltrigger.h

This lets us stop including rel.h into execnodes.h, which is a widely
used header.

src/backend/utils/adt/ri_triggers.c

@@ -48,6 +48,7 @@
 #include "utils/guc.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/rel.h"
 #include "utils/snapmgr.h"
 #include "utils/syscache.h"
 #include "utils/tqual.h"

src/backend/utils/adt/ruleutils.c

@@ -52,8 +52,9 @@
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/lsyscache.h"
-#include "utils/tqual.h"
+#include "utils/rel.h"
 #include "utils/syscache.h"
+#include "utils/tqual.h"
 #include "utils/typcache.h"
 #include "utils/xml.h"
 

src/backend/utils/adt/selfuncs.c

@@ -120,6 +120,7 @@
 #include "utils/lsyscache.h"
 #include "utils/nabstime.h"
 #include "utils/pg_locale.h"
+#include "utils/rel.h"
 #include "utils/selfuncs.h"
 #include "utils/spccache.h"
 #include "utils/syscache.h"

src/backend/utils/adt/trigfuncs.c

@@ -16,6 +16,7 @@
 #include "access/htup.h"
 #include "commands/trigger.h"
 #include "utils/builtins.h"
+#include "utils/rel.h"
 
 
 /*

src/backend/utils/adt/tsvector_op.c

@@ -25,6 +25,7 @@
 #include "tsearch/ts_utils.h"
 #include "utils/builtins.h"
 #include "utils/lsyscache.h"
+#include "utils/rel.h"
 
 
 typedef struct

src/backend/utils/adt/xml.c

@@ -74,6 +74,7 @@
 #include "utils/datetime.h"
 #include "utils/lsyscache.h"
 #include "utils/memutils.h"
+#include "utils/rel.h"
 #include "utils/syscache.h"
 #include "utils/xml.h"