Put back important code that went missing in the 8.3 merge.
Put back important code that went missing in the 8.3 merge.

Without this, a standby server gets stuck in an infinite loop, trying to
recover from a file in pg_xlog. It will also quickly fill all available disk
space by printing "record with zero len" messages in the log.

Reported off-list by Michael Kent, analysis by Amil Khanzada, Jimmy Yih, and
others.

rvs/gpdb,edespino/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,Quikling/gpdb,50wu/gpdb,xinzweb/gpdb,cjcjameson/gpdb,jmcatamney/gpdb,xinzweb/gpdb,rvs/gpdb,Chibin/gpdb,Chibin/gpdb,lisakowen/gpdb,edespino/gpdb,xinzweb/gpdb,adam8157/gpdb,edespino/gpdb,rvs/gpdb,lintzc/gpdb,50wu/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,Chibin/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,edespino/gpdb,jmcatamney/gpdb,janebeckman/gpdb,adam8157/gpdb,kaknikhil/gpdb,Quikling/gpdb,adam8157/gpdb,lintzc/gpdb,kaknikhil/gpdb,edespino/gpdb,edespino/gpdb,yuanzhao/gpdb,janebeckman/gpdb,Chibin/gpdb,yuanzhao/gpdb,adam8157/gpdb,yuanzhao/gpdb,rvs/gpdb,kaknikhil/gpdb,lintzc/gpdb,rvs/gpdb,rvs/gpdb,janebeckman/gpdb,Quikling/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,rvs/gpdb,kaknikhil/gpdb,janebeckman/gpdb,Quikling/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,edespino/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,lintzc/gpdb,kaknikhil/gpdb,xinzweb/gpdb,adam8157/gpdb,yuanzhao/gpdb,janebeckman/gpdb,lisakowen/gpdb,cjcjameson/gpdb,50wu/gpdb,ashwinstar/gpdb,lisakowen/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,lisakowen/gpdb,kaknikhil/gpdb,kaknikhil/gpdb,Quikling/gpdb,50wu/gpdb,Quikling/gpdb,cjcjameson/gpdb,lintzc/gpdb,xinzweb/gpdb,rvs/gpdb,ashwinstar/gpdb,rvs/gpdb,ashwinstar/gpdb,Quikling/gpdb,Chibin/gpdb,edespino/gpdb,adam8157/gpdb,edespino/gpdb,janebeckman/gpdb,yuanzhao/gpdb,janebeckman/gpdb,Quikling/gpdb,Chibin/gpdb,Chibin/gpdb,Chibin/gpdb,Quikling/gpdb,lintzc/gpdb,yuanzhao/gpdb,Chibin/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,rvs/gpdb,Chibin/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,edespino/gpdb,jmcatamney/gpdb,janebeckman/gpdb,cjcjameson/gpdb,50wu/gpdb,janebeckman/gpdb,Quikling/gpdb,lintzc/gpdb,greenplum-db/gpdb,50wu/gpdb,kaknikhil/gpdb,janebeckman/gpdb,ashwinstar/gpdb,lintzc/gpdb,xinzweb/gpdb,lisakowen/gpdb,adam8157/gpdb,lintzc/gpdb