BUG #15112: Unable to run pg_upgrade with earthdistance extension

The following bug has been logged on the website:

Bug reference:      15112
Logged by:          Keiko Oda
Email address:      keiko713@gmail.com
PostgreSQL version: 10.3
Operating system:   Ubuntu
Description:

This is similar to the bug report from 2016
(https://www.postgresql.org/message-id/20161015001424.1413.93990@wrigleys.postgresql.org).
where earthdistance extension is assuming that it's executed with public
schema in search_path.

With 10.3 release, Postgres has tighten the search_path during pg_upgrade
only to pg_catalog. This is problematic as it's now impossible to run
pg_upgrade with earthdistance extension (it fails with create index with
ll_to_earth function).
Prior to this, we were at least able to workaround by adding public schema
in search_path with pg_upgrade.

As it's recommended in the release note, earthdistance should adjust these
functions to not assume anything about what search path they are invoked
under.