Fix cross-version pg_dump for aggregate combine functions.

Fixes a defect in commit a7de3dc5.

David Rowley, per report from Jeff Janes, who also checked that the
fix works.

src/bin/pg_dump/pg_dump.c

@@ -12454,8 +12454,8 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 	{
 		appendPQExpBuffer(query, "SELECT aggtransfn, "
 						  "aggfinalfn, aggtranstype::pg_catalog.regtype, "
-						  "aggmtransfn, aggminvtransfn, aggmfinalfn, "
-						  "aggmtranstype::pg_catalog.regtype, "
+						  "'-' AS aggcombinefn, aggmtransfn, aggminvtransfn, "
+						  "aggmfinalfn, aggmtranstype::pg_catalog.regtype, "
 						  "aggfinalextra, aggmfinalextra, "
 						  "aggsortop::pg_catalog.regoperator, "
 						  "(aggkind = 'h') AS hypothetical, "
@@ -12473,9 +12473,10 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 	{
 		appendPQExpBuffer(query, "SELECT aggtransfn, "
 						  "aggfinalfn, aggtranstype::pg_catalog.regtype, "
-						  "'-' AS aggmtransfn, '-' AS aggminvtransfn, "
-						  "'-' AS aggmfinalfn, 0 AS aggmtranstype, "
-						  "false AS aggfinalextra, false AS aggmfinalextra, "
+						  "'-' AS aggcombinefn, '-' AS aggmtransfn, "
+						  "'-' AS aggminvtransfn, '-' AS aggmfinalfn, "
+						  "0 AS aggmtranstype, false AS aggfinalextra, "
+						  "false AS aggmfinalextra, "
 						  "aggsortop::pg_catalog.regoperator, "
 						  "false AS hypothetical, "
 						  "0 AS aggtransspace, agginitval, "
@@ -12492,9 +12493,10 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 	{
 		appendPQExpBuffer(query, "SELECT aggtransfn, "
 						  "aggfinalfn, aggtranstype::pg_catalog.regtype, "
-						  "'-' AS aggmtransfn, '-' AS aggminvtransfn, "
-						  "'-' AS aggmfinalfn, 0 AS aggmtranstype, "
-						  "false AS aggfinalextra, false AS aggmfinalextra, "
+						  "'-' AS aggcombinefn, '-' AS aggmtransfn, "
+						  "'-' AS aggminvtransfn, '-' AS aggmfinalfn, "
+						  "0 AS aggmtranstype, false AS aggfinalextra, "
+						  "false AS aggmfinalextra, "
 						  "aggsortop::pg_catalog.regoperator, "
 						  "false AS hypothetical, "
 						  "0 AS aggtransspace, agginitval, "
@@ -12509,10 +12511,10 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 	{
 		appendPQExpBuffer(query, "SELECT aggtransfn, "
 						  "aggfinalfn, aggtranstype::pg_catalog.regtype, "
-						  "'-' AS aggmtransfn, '-' AS aggminvtransfn, "
-						  "'-' AS aggmfinalfn, 0 AS aggmtranstype, "
-						  "false AS aggfinalextra, false AS aggmfinalextra, "
-						  "0 AS aggsortop, "
+						  "'-' AS aggcombinefn, '-' AS aggmtransfn, "
+						  "'-' AS aggminvtransfn, '-' AS aggmfinalfn, "
+						  "0 AS aggmtranstype, false AS aggfinalextra, "
+						  "false AS aggmfinalextra, 0 AS aggsortop, "
 						  "false AS hypothetical, "
 						  "0 AS aggtransspace, agginitval, "
 						  "0 AS aggmtransspace, NULL AS aggminitval, "
@@ -12526,10 +12528,10 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 	{
 		appendPQExpBuffer(query, "SELECT aggtransfn, aggfinalfn, "
 						  "format_type(aggtranstype, NULL) AS aggtranstype, "
-						  "'-' AS aggmtransfn, '-' AS aggminvtransfn, "
-						  "'-' AS aggmfinalfn, 0 AS aggmtranstype, "
-						  "false AS aggfinalextra, false AS aggmfinalextra, "
-						  "0 AS aggsortop, "
+						  "'-' AS aggcombinefn, '-' AS aggmtransfn, "
+						  "'-' AS aggminvtransfn, '-' AS aggmfinalfn, "
+						  "0 AS aggmtranstype, false AS aggfinalextra, "
+						  "false AS aggmfinalextra, 0 AS aggsortop, "
 						  "false AS hypothetical, "
 						  "0 AS aggtransspace, agginitval, "
 						  "0 AS aggmtransspace, NULL AS aggminitval, "
@@ -12543,10 +12545,10 @@ dumpAgg(Archive *fout, AggInfo *agginfo)
 		appendPQExpBuffer(query, "SELECT aggtransfn1 AS aggtransfn, "
 						  "aggfinalfn, "
 						  "(SELECT typname FROM pg_type WHERE oid = aggtranstype1) AS aggtranstype, "
-						  "'-' AS aggmtransfn, '-' AS aggminvtransfn, "
-						  "'-' AS aggmfinalfn, 0 AS aggmtranstype, "
-						  "false AS aggfinalextra, false AS aggmfinalextra, "
-						  "0 AS aggsortop, "
+						  "'-' AS aggcombinefn, '-' AS aggmtransfn, "
+						  "'-' AS aggminvtransfn, '-' AS aggmfinalfn, "
+						  "0 AS aggmtranstype, false AS aggfinalextra, "
+						  "false AS aggmfinalextra, 0 AS aggsortop, "
 						  "false AS hypothetical, "
 						  "0 AS aggtransspace, agginitval1 AS agginitval, "
 						  "0 AS aggmtransspace, NULL AS aggminitval, "