Don't dump views for Postgres extensions

If a database view has the same name as a database extension, we want to
ignore that view and not dump it with the rest of the schema. (The
extension will already be handled through the schema's
`enable_extension` statement.) This approach will handle system views
from extensions like PostGIS whose views do not begin with `pg_`.

WIP

lib/scenic/adapters/postgres.rb

@@ -6,6 +6,7 @@ def self.views
           SELECT viewname, definition
           FROM pg_views
           WHERE schemaname = ANY (current_schemas(false))
+          AND viewname NOT IN (SELECT extname FROM pg_extension)
         SQL
       end