Fix performance bug in constant-expression simplifier.  After finding that the inputs to a given operator can be recursively simplified to constants, it was evaluating the operator using the op's *original* (unsimplified) arg list, so that any subexpressions had to be evaluated again.  A constant subexpression at depth N got evaluated N times. Probably not very important in practical situations, but it made us look real slow in MySQL's 'crashme' test...
Fix performance bug in constant-expression simplifier.  After finding
that the inputs to a given operator can be recursively simplified to
constants, it was evaluating the operator using the op's *original*
(unsimplified) arg list, so that any subexpressions had to be evaluated
again.  A constant subexpression at depth N got evaluated N times.
Probably not very important in practical situations, but it made us look
real slow in MySQL's 'crashme' test...

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