Fix WAL-logging of ALTER TABLE SET TABLESPACE.

Since we have backported streaming replication from PostgreSQL 9.0, we
need to use XLogIsNeeded() rather than XLogArchivingActive(), to determine
if WAL-logging is needed.

This explains the 'CS_switch' TINC test failure.

src/backend/commands/tablecmds.c

@@ -10365,12 +10365,6 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
 	BlockNumber nblocks;
 	BlockNumber blkno;
 
-	/*
-	 * We need to log the copied data in WAL iff WAL archiving is enabled AND
-	 * it's not a temp rel.
-	 */
-	use_wal = XLogArchivingActive() && !istemp;
-
 	/*
 	 * palloc the buffer so that it's MAXALIGN'd.  If it were just a local
 	 * char[] array, the compiler might align it on any byte boundary, which
@@ -10380,6 +10374,12 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
 	buf = (char *) palloc(BLCKSZ);
 	page = (Page) buf;
 
+	/*
+	 * We need to log the copied data in WAL iff WAL archiving/streaming is
+	 * enabled AND it's not a temp rel.
+	 */
+	use_wal = XLogIsNeeded() && !istemp;
+
 	nblocks = smgrnblocks(src, forkNum);
 
 	for (blkno = 0; blkno < nblocks; blkno++)