Reduce PANIC to ERROR in several xlog routines that are used in both critical and noncritical contexts (an example of noncritical being post-checkpoint removal of dead xlog segments).  In the critical cases the CRIT_SECTION mechanism will cause ERROR to be promoted to PANIC anyway, and in the noncritical cases we shouldn't let an error take down the entire database.  Arguably there should be *no* explicit PANIC errors in this module, only more START/END_CRIT_SECTION calls, but I didn't go that far.  (Yet.)
Reduce PANIC to ERROR in several xlog routines that are used in both
critical and noncritical contexts (an example of noncritical being
post-checkpoint removal of dead xlog segments).  In the critical cases
the CRIT_SECTION mechanism will cause ERROR to be promoted to PANIC
anyway, and in the noncritical cases we shouldn't let an error take
down the entire database.  Arguably there should be *no* explicit
PANIC errors in this module, only more START/END_CRIT_SECTION calls,
but I didn't go that far.  (Yet.)

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