Allow units to be specified with configuration settings.

Allow units to be specified with configuration settings.

The bulk of the code for this feature is stolen from PostgreSQL source
so making the pgpool configuration file syntax more inline with that of PG's

Similarly, PGPOOL SHOW command now outputs units along with value

postgres=# pgpool show search_primary_node_timeout;
search_primary_node_timeout
-----------------------------
5min
(1 row)