Ensure no xid gaps during Hot Standby startup

Simon Riggs <simon@2ndQuadrant.com>

Commit: a41c88194b19655d7f2cb556d0fdada227dea941
Author: Simon Riggs <simon@2ndQuadrant.com>
Date: 2013-06-23T13:50:17Z
Releases: 9.1.10
Ensure no xid gaps during Hot Standby startup

In some cases with higher numbers of subtransactions
it was possible for us to incorrectly initialize
subtrans leading to complaints of missing pages.

Bug report by Sergey Konoplev
Analysis and fix by Andres Freund

Files