databases/pgpool: Update from 3.4.25 to 3.4.26 and deprecated the port

Enhancements

• Import some of memory manager debug facilities from PostgreSQL. (Tatsuo Ishii)
• Use pg_get_expr() instead of pg_attrdef.adsrc to support for PostgreSQL 12. (Bo Peng)
• Enhance shutdown script of pgpool_setup. (Tatsuo Ishii)
  • Make shutdownall to wait for completion of shutdown of Pgpool-II.
  • If environment variable CHECK_TIME_WAIT is set to true, use netstat command to confirm usage of the TCP/IP port while executing shutdown script.
• Deal pgpool_adm extension with PostgreSQL 12. (Tatsuo Ishii)

Bug fixes

• Fix pgpool_setup to produce correct follow master command. (Tatsuo Ishii)
• Fix query cache module so that it checks oid array's bound. (Tatsuo Ishii)
• Fix off-by-one error in query cache module. (Tatsuo Ishii)
• Fix segfault when samenet is specified in pool_hba.conf. (Tatsuo Ishii)
• Fix to deal with backslashes according to the config of standard_conforming_strings in native replication mode. (bug 467) (Bo Peng)
• Fix memory leaks. (Tatsuo Ishii)

Changelog taken from: https://www.pgpool.net/docs/latest/en/html/release-3-4-25.html

Also set DEPRECATED and EXPIRATION_DATE because the port reached its EOL at 2019-08-15. This will give possible user a short time period for an update and also warn them.