Phase 1 of fix for 'SMgrRelation hashtable corrupted' problem. This

is the minimum required fix.  I want to look next at taking advantage of
it by simplifying the message semantics in the shared inval message queue,
but that part can be held over for 8.1 if it turns out too ugly.

src/backend/postmaster/bgwriter.c

@@ -37,7 +37,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.12 2004/12/31 22:00:40 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/postmaster/bgwriter.c,v 1.13 2005/01/10 20:02:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -349,9 +349,7 @@ BackgroundWriterMain(void)
 			/*
 			 * After any checkpoint, close all smgr files.	This is so we
 			 * won't hang onto smgr references to deleted files
-			 * indefinitely. (It is safe to do this because this process
-			 * does not have a relcache, and so no dangling references
-			 * could remain.)
+			 * indefinitely.
 			 */
 			smgrcloseall();