Allow bare column names to be subscripted as arrays.  This creates a reduce/reduce conflict, which I resolved by changing the 'AexprConst -> Typename Sconst' rule to 'AexprConst -> SimpleTypename Sconst'. In other words, a subscripted type declaration can't be used in that syntax any longer.  This seems a small price to pay for not having to qualify subscripted columns anymore. Other cleanups: rename res_target_list to update_target_list, and remove productions for variants that are not legal in an UPDATE target list; rename res_target_list2 to plain target_list; delete position_expr in favor of using b_expr in that production; merge opt_indirection into attr nonterminal, since there are no places where an unsubscripted attr is wanted; fix typos in Param support; change case_arg so that an arbitrary a_expr is allowed, not only a column name.
Allow bare column names to be subscripted as arrays.  This
creates a reduce/reduce conflict, which I resolved by changing the
'AexprConst -> Typename Sconst' rule to 'AexprConst -> SimpleTypename Sconst'.
In other words, a subscripted type declaration can't be used in that
syntax any longer.  This seems a small price to pay for not having to
qualify subscripted columns anymore.
Other cleanups: rename res_target_list to update_target_list, and remove
productions for variants that are not legal in an UPDATE target list;
rename res_target_list2 to plain target_list; delete position_expr
in favor of using b_expr in that production; merge opt_indirection
into attr nonterminal, since there are no places where an unsubscripted
attr is wanted; fix typos in Param support; change case_arg so that
an arbitrary a_expr is allowed, not only a column name.

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