Fix postmaster to attempt restart after a hot-standby crash.
Fix postmaster to attempt restart after a hot-standby crash.

The postmaster was coded to treat any unexpected exit of the startup
process (i.e., the WAL replay process) as a catastrophic crash, and not try
to restart it. This was OK so long as the startup process could not have
any sibling postmaster children.  However, if a hot-standby backend
crashes, we SIGQUIT the startup process along with everything else, and the
resulting exit is hardly "unexpected".  Treating it as such meant we failed
to restart a standby server after any child crash at all, not only a crash
of the WAL replay process as intended.  Adjust that.  Back-patch to 9.0
where hot standby was introduced.

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