Add documentation example of using interval multiplication with 'days'.
Add documentation example of using interval multiplication with 'days'.

Backpatch to 8.1.X.

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