PostgreSQL 13 beta1 support.

There don't appear to be any behavioral changes since PostgreSQL 12 and all the tests pass.

Changes to the control/catalog/WAL versions in subsequent betas may break compatibility but pgBackRest will be updated with each release to keep pace.

src/postgres/interface.c

@@ -110,6 +110,23 @@ typedef struct PgInterface
 
 static const PgInterface pgInterface[] =
 {
+    {
+        .version = PG_VERSION_13,
+
+        .catalogVersion = pgInterfaceCatalogVersion130,
+
+        .controlIs = pgInterfaceControlIs130,
+        .control = pgInterfaceControl130,
+        .controlVersion = pgInterfaceControlVersion130,
+
+        .walIs = pgInterfaceWalIs130,
+        .wal = pgInterfaceWal130,
+
+#ifdef DEBUG
+        .controlTest = pgInterfaceControlTest130,
+        .walTest = pgInterfaceWalTest130,
+#endif
+    },
     {
         .version = PG_VERSION_12,