Add "topology" to the default search_path of topology-enabled DBs

[strk]

We want "topology" to be in the default path of databases with topology installed. This will make function overrides work smoothly. See #1289.

ALTER DATABASE current_db() SET search_path ....

We'll likely need a function for doing the _append_ part (can't append in SQL I'm afraid)

[robe]

Done at r8197. It should do it for both new installs and when running the generated topology_upgrade_20_minor.sql

[strk]

It did it for sure on new install, see r8201. Thanks a lot !