Fix check for superuser_reserved_connections.

Upstream uses >= here. It was changed in GPDB, to use > instead of >=. but
I don't see how that's more correct or better. I tracked that change in
the old pre-open-sourcing repository to this commit:

commit f3e98a1ef5fc5915662077b137c563371ea1c0a4
Date: Mon Apr 6 15:04:33 2009 -0800

   Fixed guc check for ReservedBackends.

   [git-p4: depot-paths = "//cdb2/main/": change = 33269]

So, there was no explanation there either, what the alleged problem was.

src/backend/postmaster/postmaster.c

@@ -1154,7 +1154,7 @@ PostmasterMain(int argc, char *argv[])
 	/*
 	 * Check for invalid combinations of GUC settings.
 	 */
-	if (ReservedBackends > MaxBackends)
+	if (ReservedBackends >= MaxBackends)
 	{
 		write_stderr("%s: superuser_reserved_connections must be less than max_connections\n", progname);
 		ExitPostmaster(1);