Clean up build errors when creating/recreating database schema

Clean up build errors when creating/recreating database schema

Dropping the evergreen schema cascaded and wiped out some previously
defined functions, so move it ahead of the other functions. (And maybe
we can start moving those public functions into the evergreen schema?)

DROP AGGREGATE IF EXISTS exists on any version of PostgreSQL that we
care about for Evergreen 2.0, so we can use it to avoid false errors
during schema creation.

FTS config was complaining about public.english_nostop in the ALTER
statement, so remove the schema qualification. This seems to have
been there for a long time?

Use IF EXISTS when dropping the unapi schema to avoid an error.

git-svn-id: svn://svn.open-ils.org/ILS/branches/rel_2_1@19722 dcc99617-32d9-48b4-a31d-7c20da2025e4