Fix syslogger's rotation disable/re-enable logic.
Fix syslogger's rotation disable/re-enable logic.

If it fails to open a new log file, the syslogger assumes there's something
wrong with its parameters (such as log_directory), and stops attempting
automatic time-based or size-based log file rotations.  Sending it SIGHUP
is supposed to start that up again.  However, the original coding for that
was really bogus, involving clobbering a couple of GUC variables and hoping
that SIGHUP processing would restore them.  Get rid of that technique in
favor of maintaining a separate flag showing we've turned rotation off.
Per report from Mark Kirkwood.

Also, the syslogger will automatically attempt to create the log_directory
directory if it doesn't exist, but that was only happening at startup.
For consistency and ease of use, it should do the same whenever the value
of log_directory is changed by SIGHUP.

Back-patch to all supported branches.

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