Merge pull request #25 from alexeyklyukin/master

Add support for archive_cleanup_command for PostgreSQL 9.0 and above.
Merge pull request #26 from alexeyklyukin/master

Bug fix
Make sure that l_archivedir, when it exists, is accessible and empty before creating subdirectories for the standby.
Also show WARNING if l_archivedir exists and is empty.
Add support for 2 new parameters: pg_hba_conf_failover and postgresql_conf_failover, that will play the same role as former pg_hba_conf and postgresql_conf. Parameter names w/o the failover suffix  will be repurposed to copy configuration files when the standby enters the standby mode (-S), since those files are not rsynced from the primary.
Copy configuration files for both normal and failover standby.

On the normal startup, postgresql_conf and pg_hba_conf options are
used. For the failover, it switches to the _failover counterparts.
In both cases, cmd_standby only attempts to copy files that exist
and readable.

Additionally, when no_copy_conf is set, add an option to use
pg_hba_conf file.