Don't trash input list structure in does_not_exist_skipping().
Don't trash input list structure in does_not_exist_skipping().

The trigger and rule cases need to split up the input name list, but
they mustn't corrupt the passed-in data structure, since it could be part
of a cached utility-statement parsetree.  Per bug #7641.

ashwinstar/gpdb,50wu/gpdb,pavanvd/postgres-xl,Postgres-XL/Postgres-XL,zeroae/postgres-xl,pavanvd/postgres-xl,jmcatamney/gpdb,jmcatamney/gpdb,adam8157/gpdb,adam8157/gpdb,jmcatamney/gpdb,50wu/gpdb,lisakowen/gpdb,ovr/postgres-xl,greenplum-db/gpdb,ovr/postgres-xl,yazun/postgres-xl,ashwinstar/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,greenplum-db/gpdb,oberstet/postgres-xl,yazun/postgres-xl,adam8157/gpdb,Postgres-XL/Postgres-XL,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,lisakowen/gpdb,xinzweb/gpdb,adam8157/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,techdragon/Postgres-XL,ovr/postgres-xl,lisakowen/gpdb,xinzweb/gpdb,Postgres-XL/Postgres-XL,oberstet/postgres-xl,50wu/gpdb,lisakowen/gpdb,techdragon/Postgres-XL,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,pavanvd/postgres-xl,techdragon/Postgres-XL,ashwinstar/gpdb,greenplum-db/gpdb,lisakowen/gpdb,jmcatamney/gpdb,ashwinstar/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,yazun/postgres-xl,ovr/postgres-xl,adam8157/gpdb,zeroae/postgres-xl,Postgres-XL/Postgres-XL,adam8157/gpdb,xinzweb/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,yazun/postgres-xl,adam8157/gpdb,zeroae/postgres-xl,xinzweb/gpdb,50wu/gpdb,jmcatamney/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,greenplum-db/gpdb,lisakowen/gpdb,zeroae/postgres-xl,pavanvd/postgres-xl,oberstet/postgres-xl,jmcatamney/gpdb,greenplum-db/gpdb,yazun/postgres-xl,ovr/postgres-xl,50wu/gpdb,adam8157/gpdb,oberstet/postgres-xl,zeroae/postgres-xl