Add comment about checkpoint panic behavior during shutdown, per suggestion from Qingqing Zhou.
Add comment about checkpoint panic behavior during shutdown, per
suggestion from Qingqing Zhou.

royc1/gpdb,ashwinstar/gpdb,yazun/postgres-xl,kmjungersen/PostgresXL,Chibin/gpdb,CraigHarris/gpdb,Quikling/gpdb,tangp3/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,CraigHarris/gpdb,chrishajas/gpdb,rubikloud/gpdb,cjcjameson/gpdb,postmind-net/postgres-xl,janebeckman/gpdb,xinzweb/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,ovr/postgres-xl,lintzc/gpdb,edespino/gpdb,yuanzhao/gpdb,zaksoup/gpdb,xuegang/gpdb,randomtask1155/gpdb,randomtask1155/gpdb,postmind-net/postgres-xl,chrishajas/gpdb,rubikloud/gpdb,arcivanov/postgres-xl,CraigHarris/gpdb,royc1/gpdb,yuanzhao/gpdb,Postgres-XL/Postgres-XL,jmcatamney/gpdb,Chibin/gpdb,ovr/postgres-xl,arcivanov/postgres-xl,chrishajas/gpdb,Quikling/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,foyzur/gpdb,cjcjameson/gpdb,edespino/gpdb,tpostgres-projects/tPostgres,royc1/gpdb,ahachete/gpdb,Quikling/gpdb,lintzc/gpdb,foyzur/gpdb,royc1/gpdb,janebeckman/gpdb,janebeckman/gpdb,jmcatamney/gpdb,adam8157/gpdb,yazun/postgres-xl,greenplum-db/gpdb,pavanvd/postgres-xl,50wu/gpdb,lintzc/gpdb,janebeckman/gpdb,lintzc/gpdb,janebeckman/gpdb,kaknikhil/gpdb,lintzc/gpdb,arcivanov/postgres-xl,jmcatamney/gpdb,royc1/gpdb,rvs/gpdb,Quikling/gpdb,techdragon/Postgres-XL,jmcatamney/gpdb,foyzur/gpdb,lintzc/gpdb,chrishajas/gpdb,rubikloud/gpdb,lisakowen/gpdb,xinzweb/gpdb,tpostgres-projects/tPostgres,jmcatamney/gpdb,Postgres-XL/Postgres-XL,cjcjameson/gpdb,0x0FFF/gpdb,randomtask1155/gpdb,pavanvd/postgres-xl,CraigHarris/gpdb,Quikling/gpdb,zeroae/postgres-xl,arcivanov/postgres-xl,jmcatamney/gpdb,tangp3/gpdb,xinzweb/gpdb,xinzweb/gpdb,atris/gpdb,ovr/postgres-xl,adam8157/gpdb,postmind-net/postgres-xl,edespino/gpdb,edespino/gpdb,snaga/postgres-xl,Chibin/gpdb,janebeckman/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,foyzur/gpdb,kaknikhil/gpdb,rvs/gpdb,50wu/gpdb,adam8157/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,50wu/gpdb,foyzur/gpdb,techdragon/Postgres-XL,kmjungersen/PostgresXL,Chibin/gpdb,0x0FFF/gpdb,atris/gpdb,lisakowen/gpdb,adam8157/gpdb,atris/gpdb,ahachete/gpdb,kaknikhil/gpdb,CraigHarris/gpdb,rvs/gpdb,rubikloud/gpdb,zaksoup/gpdb,xuegang/gpdb,adam8157/gpdb,greenplum-db/gpdb,zaksoup/gpdb,kmjungersen/PostgresXL,lisakowen/gpdb,edespino/gpdb,pavanvd/postgres-xl,Quikling/gpdb,zeroae/postgres-xl,edespino/gpdb,0x0FFF/gpdb,tangp3/gpdb,Chibin/gpdb,rubikloud/gpdb,adam8157/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,CraigHarris/gpdb,oberstet/postgres-xl,lpetrov-pivotal/gpdb,lisakowen/gpdb,zaksoup/gpdb,atris/gpdb,Postgres-XL/Postgres-XL,rvs/gpdb,ahachete/gpdb,xuegang/gpdb,lisakowen/gpdb,greenplum-db/gpdb,cjcjameson/gpdb,tangp3/gpdb,yazun/postgres-xl,rvs/gpdb,50wu/gpdb,ashwinstar/gpdb,lpetrov-pivotal/gpdb,zeroae/postgres-xl,janebeckman/gpdb,lintzc/gpdb,pavanvd/postgres-xl,zaksoup/gpdb,Chibin/gpdb,0x0FFF/gpdb,royc1/gpdb,cjcjameson/gpdb,Quikling/gpdb,cjcjameson/gpdb,atris/gpdb,ahachete/gpdb,ashwinstar/gpdb,randomtask1155/gpdb,lpetrov-pivotal/gpdb,xinzweb/gpdb,xuegang/gpdb,xuegang/gpdb,tpostgres-projects/tPostgres,ahachete/gpdb,lpetrov-pivotal/gpdb,atris/gpdb,foyzur/gpdb,tangp3/gpdb,Postgres-XL/Postgres-XL,yazun/postgres-xl,zaksoup/gpdb,cjcjameson/gpdb,janebeckman/gpdb,lintzc/gpdb,ovr/postgres-xl,yuanzhao/gpdb,atris/gpdb,ovr/postgres-xl,Quikling/gpdb,royc1/gpdb,tpostgres-projects/tPostgres,chrishajas/gpdb,xinzweb/gpdb,ahachete/gpdb,xuegang/gpdb,jmcatamney/gpdb,techdragon/Postgres-XL,chrishajas/gpdb,pavanvd/postgres-xl,snaga/postgres-xl,kaknikhil/gpdb,rvs/gpdb,rubikloud/gpdb,kaknikhil/gpdb,CraigHarris/gpdb,edespino/gpdb,atris/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,kmjungersen/PostgresXL,kaknikhil/gpdb,yazun/postgres-xl,yuanzhao/gpdb,lisakowen/gpdb,postmind-net/postgres-xl,xuegang/gpdb,foyzur/gpdb,royc1/gpdb,randomtask1155/gpdb,kmjungersen/PostgresXL,oberstet/postgres-xl,zeroae/postgres-xl,tpostgres-projects/tPostgres,50wu/gpdb,edespino/gpdb,kaknikhil/gpdb,snaga/postgres-xl,tangp3/gpdb,ashwinstar/gpdb,rvs/gpdb,50wu/gpdb,snaga/postgres-xl,zeroae/postgres-xl,lisakowen/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,zaksoup/gpdb,Quikling/gpdb,chrishajas/gpdb,lpetrov-pivotal/gpdb,rvs/gpdb,postmind-net/postgres-xl,oberstet/postgres-xl,cjcjameson/gpdb,CraigHarris/gpdb,tangp3/gpdb,50wu/gpdb,foyzur/gpdb,randomtask1155/gpdb,rubikloud/gpdb,lintzc/gpdb,adam8157/gpdb,greenplum-db/gpdb,rvs/gpdb,lpetrov-pivotal/gpdb,janebeckman/gpdb,0x0FFF/gpdb,50wu/gpdb,edespino/gpdb,techdragon/Postgres-XL,randomtask1155/gpdb,tangp3/gpdb,lisakowen/gpdb,ahachete/gpdb,arcivanov/postgres-xl,greenplum-db/gpdb,lpetrov-pivotal/gpdb,kaknikhil/gpdb,edespino/gpdb,xuegang/gpdb,xinzweb/gpdb,randomtask1155/gpdb,yuanzhao/gpdb,techdragon/Postgres-XL,snaga/postgres-xl,greenplum-db/gpdb,arcivanov/postgres-xl,rvs/gpdb,janebeckman/gpdb,ahachete/gpdb,Chibin/gpdb,cjcjameson/gpdb,Quikling/gpdb,chrishajas/gpdb,adam8157/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,oberstet/postgres-xl,yuanzhao/gpdb,zaksoup/gpdb,rubikloud/gpdb,xuegang/gpdb,Chibin/gpdb,Chibin/gpdb,kaknikhil/gpdb,Chibin/gpdb,CraigHarris/gpdb,xinzweb/gpdb,lpetrov-pivotal/gpdb