Make pgstatindex respond to cancel interrupts.
Make pgstatindex respond to cancel interrupts.

A similar problem for pgstattuple() was fixed in April of 2010 by commit
33065ef8bc52253ae855bc959576e52d8a28ba06, but pgstatindex() seems to have
been overlooked.

Back-patch all the way, as with that commit, though not to 7.4 through
8.1, since those are now EOL.

jmcatamney/gpdb,50wu/gpdb,kmjungersen/PostgresXL,techdragon/Postgres-XL,jmcatamney/gpdb,adam8157/gpdb,tpostgres-projects/tPostgres,yazun/postgres-xl,Postgres-XL/Postgres-XL,lisakowen/gpdb,pavanvd/postgres-xl,oberstet/postgres-xl,yazun/postgres-xl,ovr/postgres-xl,ashwinstar/gpdb,jmcatamney/gpdb,snaga/postgres-xl,tpostgres-projects/tPostgres,ovr/postgres-xl,adam8157/gpdb,xinzweb/gpdb,postmind-net/postgres-xl,zeroae/postgres-xl,pavanvd/postgres-xl,zeroae/postgres-xl,ovr/postgres-xl,kmjungersen/PostgresXL,techdragon/Postgres-XL,50wu/gpdb,adam8157/gpdb,ashwinstar/gpdb,arcivanov/postgres-xl,yazun/postgres-xl,postmind-net/postgres-xl,Postgres-XL/Postgres-XL,arcivanov/postgres-xl,ovr/postgres-xl,Postgres-XL/Postgres-XL,lisakowen/gpdb,ashwinstar/gpdb,arcivanov/postgres-xl,jmcatamney/gpdb,snaga/postgres-xl,oberstet/postgres-xl,lisakowen/gpdb,xinzweb/gpdb,snaga/postgres-xl,greenplum-db/gpdb,lisakowen/gpdb,arcivanov/postgres-xl,adam8157/gpdb,kmjungersen/PostgresXL,yazun/postgres-xl,xinzweb/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,xinzweb/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,postmind-net/postgres-xl,ashwinstar/gpdb,lisakowen/gpdb,snaga/postgres-xl,kmjungersen/PostgresXL,postmind-net/postgres-xl,lisakowen/gpdb,ashwinstar/gpdb,snaga/postgres-xl,50wu/gpdb,pavanvd/postgres-xl,50wu/gpdb,tpostgres-projects/tPostgres,jmcatamney/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,oberstet/postgres-xl,arcivanov/postgres-xl,yazun/postgres-xl,tpostgres-projects/tPostgres,techdragon/Postgres-XL,Postgres-XL/Postgres-XL,zeroae/postgres-xl,jmcatamney/gpdb,50wu/gpdb,oberstet/postgres-xl,jmcatamney/gpdb,lisakowen/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,tpostgres-projects/tPostgres,jmcatamney/gpdb,pavanvd/postgres-xl,ashwinstar/gpdb,greenplum-db/gpdb,50wu/gpdb,greenplum-db/gpdb,pavanvd/postgres-xl,kmjungersen/PostgresXL,techdragon/Postgres-XL,xinzweb/gpdb,Postgres-XL/Postgres-XL,greenplum-db/gpdb,arcivanov/postgres-xl,xinzweb/gpdb,adam8157/gpdb,adam8157/gpdb,greenplum-db/gpdb,ovr/postgres-xl,50wu/gpdb,adam8157/gpdb,xinzweb/gpdb,lisakowen/gpdb,oberstet/postgres-xl,postmind-net/postgres-xl,adam8157/gpdb,xinzweb/gpdb