Fix crash-recovery of B-tree split records.
Fix crash-recovery of B-tree split records.

Merge of upstream B-tree split WAL-logging changes, broke the recovery
incase of Btree split. The MirroredLock needs to held while manipulating
buffer.

50wu/gpdb,adam8157/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,cjcjameson/gpdb,yuanzhao/gpdb,janebeckman/gpdb,xuegang/gpdb,0x0FFF/gpdb,atris/gpdb,janebeckman/gpdb,0x0FFF/gpdb,50wu/gpdb,edespino/gpdb,zaksoup/gpdb,edespino/gpdb,cjcjameson/gpdb,rvs/gpdb,xinzweb/gpdb,50wu/gpdb,xuegang/gpdb,zaksoup/gpdb,atris/gpdb,adam8157/gpdb,greenplum-db/gpdb,Quikling/gpdb,ahachete/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,adam8157/gpdb,zaksoup/gpdb,ahachete/gpdb,jmcatamney/gpdb,kaknikhil/gpdb,lisakowen/gpdb,randomtask1155/gpdb,rubikloud/gpdb,greenplum-db/gpdb,lpetrov-pivotal/gpdb,yuanzhao/gpdb,edespino/gpdb,adam8157/gpdb,foyzur/gpdb,foyzur/gpdb,CraigHarris/gpdb,edespino/gpdb,atris/gpdb,Chibin/gpdb,zaksoup/gpdb,xuegang/gpdb,rvs/gpdb,ahachete/gpdb,Quikling/gpdb,lintzc/gpdb,ahachete/gpdb,edespino/gpdb,50wu/gpdb,foyzur/gpdb,greenplum-db/gpdb,edespino/gpdb,ahachete/gpdb,lpetrov-pivotal/gpdb,Chibin/gpdb,janebeckman/gpdb,rvs/gpdb,CraigHarris/gpdb,janebeckman/gpdb,lintzc/gpdb,0x0FFF/gpdb,adam8157/gpdb,ashwinstar/gpdb,ahachete/gpdb,janebeckman/gpdb,chrishajas/gpdb,CraigHarris/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,xinzweb/gpdb,randomtask1155/gpdb,50wu/gpdb,chrishajas/gpdb,kaknikhil/gpdb,Quikling/gpdb,chrishajas/gpdb,royc1/gpdb,foyzur/gpdb,xuegang/gpdb,randomtask1155/gpdb,edespino/gpdb,xinzweb/gpdb,edespino/gpdb,50wu/gpdb,foyzur/gpdb,ashwinstar/gpdb,randomtask1155/gpdb,kaknikhil/gpdb,xuegang/gpdb,tangp3/gpdb,chrishajas/gpdb,ashwinstar/gpdb,Chibin/gpdb,Chibin/gpdb,yuanzhao/gpdb,janebeckman/gpdb,xinzweb/gpdb,yuanzhao/gpdb,rvs/gpdb,yuanzhao/gpdb,rvs/gpdb,janebeckman/gpdb,tangp3/gpdb,rvs/gpdb,adam8157/gpdb,foyzur/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,Quikling/gpdb,Quikling/gpdb,greenplum-db/gpdb,royc1/gpdb,jmcatamney/gpdb,xuegang/gpdb,rvs/gpdb,atris/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,rubikloud/gpdb,lisakowen/gpdb,0x0FFF/gpdb,chrishajas/gpdb,randomtask1155/gpdb,Quikling/gpdb,CraigHarris/gpdb,tangp3/gpdb,janebeckman/gpdb,janebeckman/gpdb,edespino/gpdb,lintzc/gpdb,adam8157/gpdb,Chibin/gpdb,rubikloud/gpdb,cjcjameson/gpdb,ahachete/gpdb,jmcatamney/gpdb,janebeckman/gpdb,0x0FFF/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,atris/gpdb,Quikling/gpdb,randomtask1155/gpdb,chrishajas/gpdb,Chibin/gpdb,rubikloud/gpdb,jmcatamney/gpdb,foyzur/gpdb,lpetrov-pivotal/gpdb,cjcjameson/gpdb,lisakowen/gpdb,lpetrov-pivotal/gpdb,lisakowen/gpdb,CraigHarris/gpdb,xinzweb/gpdb,xinzweb/gpdb,kaknikhil/gpdb,royc1/gpdb,randomtask1155/gpdb,tangp3/gpdb,rubikloud/gpdb,tangp3/gpdb,atris/gpdb,lisakowen/gpdb,lintzc/gpdb,xuegang/gpdb,jmcatamney/gpdb,Quikling/gpdb,lpetrov-pivotal/gpdb,lisakowen/gpdb,Chibin/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,lpetrov-pivotal/gpdb,royc1/gpdb,greenplum-db/gpdb,rvs/gpdb,yuanzhao/gpdb,atris/gpdb,rubikloud/gpdb,ashwinstar/gpdb,chrishajas/gpdb,zaksoup/gpdb,chrishajas/gpdb,CraigHarris/gpdb,foyzur/gpdb,50wu/gpdb,kaknikhil/gpdb,cjcjameson/gpdb,zaksoup/gpdb,tangp3/gpdb,lisakowen/gpdb,royc1/gpdb,kaknikhil/gpdb,lintzc/gpdb,zaksoup/gpdb,lisakowen/gpdb,atris/gpdb,greenplum-db/gpdb,tangp3/gpdb,rubikloud/gpdb,royc1/gpdb,Quikling/gpdb,xinzweb/gpdb,kaknikhil/gpdb,rvs/gpdb,Chibin/gpdb,50wu/gpdb,rubikloud/gpdb,adam8157/gpdb,lintzc/gpdb,tangp3/gpdb,royc1/gpdb,xuegang/gpdb,xinzweb/gpdb,edespino/gpdb,ashwinstar/gpdb,lintzc/gpdb,xuegang/gpdb,0x0FFF/gpdb,Chibin/gpdb,yuanzhao/gpdb,lpetrov-pivotal/gpdb,ashwinstar/gpdb,zaksoup/gpdb,CraigHarris/gpdb,royc1/gpdb,lpetrov-pivotal/gpdb,randomtask1155/gpdb,ashwinstar/gpdb,Chibin/gpdb,ahachete/gpdb,lintzc/gpdb,Quikling/gpdb,rvs/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,lintzc/gpdb,kaknikhil/gpdb