Convert the arithmetic for shared memory size calculation from 'int'

to 'Size' (that is, size_t), and install overflow detection checks in it.
This allows us to remove the former arbitrary restrictions on NBuffers
etc.  It won't make any difference in a 32-bit machine, but in a 64-bit
machine you could theoretically have terabytes of shared buffers.
(How efficiently we could manage 'em remains to be seen.)  Similarly,
num_temp_buffers, work_mem, and maintenance_work_mem can be set above
2Gb on a 64-bit machine.  Original patch from Koichi Suzuki, additional
work by moi.

src/backend/storage/ipc/sinval.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.76 2005/05/19 21:35:46 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/sinval.c,v 1.77 2005/08/20 23:26:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -55,10 +55,10 @@ static void ProcessCatchupEvent(void);
 /*	should be called only by the POSTMASTER									*/
 /****************************************************************************/
 void
-CreateSharedInvalidationState(int maxBackends)
+CreateSharedInvalidationState(void)
 {
 	/* SInvalLock must be initialized already, during LWLock init */
-	SIBufferInit(maxBackends);
+	SIBufferInit();
 }
 
 /*