Add a few tests for unary minus syntax.
Add a few tests for unary minus syntax.

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