Add tests for unary minus.
Add tests for unary minus.

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