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/procarray.c

@@ -23,7 +23,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.5 2005/08/20 01:26:36 ishii Exp $
+ *	  $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.6 2005/08/20 23:26:20 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -81,11 +81,16 @@ static void DisplayXidCache(void);
 /*
  * Report shared-memory space needed by CreateSharedProcArray.
  */
-int
+Size
 ProcArrayShmemSize(void)
 {
-	return MAXALIGN(offsetof(ProcArrayStruct, procs) +
-					(MaxBackends + max_prepared_xacts) * sizeof(PGPROC *));
+	Size		size;
+
+	size = offsetof(ProcArrayStruct, procs);
+	size = add_size(size, mul_size(sizeof(PGPROC *),
+								   add_size(MaxBackends, max_prepared_xacts)));
+
+	return size;
 }
 
 /*