Update xindex.sgml to discuss operator families.
Update xindex.sgml to discuss operator families.

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