Fix nbtree's failure to clear BTScans list during xact abort.

Also, move responsibility for calling vc_abort into main xact.c list of
things-to-call-at-abort.  What in the world was it doing down inside of
TransactionIdAbort()?

src/backend/access/nbtree/nbtpage.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.30 1999/07/17 20:16:42 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/nbtpage.c,v 1.31 1999/08/08 20:12:50 tgl Exp $
  *
  *	NOTES
  *	   Postgres btree pages look like ordinary relation pages.	The opaque
@@ -42,7 +42,6 @@ typedef struct BTMetaPageData
 #define BTPageGetMeta(p) \
 	((BTMetaPageData *) &((PageHeader) p)->pd_linp[0])
 
-extern bool BuildingBtree;
 
 /*
  *	We use high-concurrency locking on btrees.	There are two cases in

src/backend/access/nbtree/nbtscan.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/Attic/nbtscan.c,v 1.27 1999/07/15 23:03:00 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/access/nbtree/Attic/nbtscan.c,v 1.28 1999/08/08 20:12:51 tgl Exp $
  *
  *
  * NOTES
@@ -43,6 +43,28 @@ static BTScanList BTScans = (BTScanList) NULL;
 
 static void _bt_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno);
 
+/*
+ * AtEOXact_nbtree() --- clean up nbtree subsystem at xact abort or commit.
+ *
+ * This is here because it needs to touch this module's static var BTScans.
+ */
+void
+AtEOXact_nbtree(void)
+{
+	/* Note: these actions should only be necessary during xact abort;
+	 * but they can't hurt during a commit.
+	 */
+
+	/* Reset the active-scans list to empty.
+	 * We do not need to free the list elements, because they're all
+	 * palloc()'d, so they'll go away at end of transaction anyway.
+	 */
+	BTScans = NULL;
+
+	/* If we were building a btree, we ain't anymore. */
+	BuildingBtree = false;
+}
+
 /*
  *	_bt_regscan() -- register a new scan.
  */